Video GPU port adapters can be easy or pure H3LL.        
                   The worst involve DVI, In some odd ways seen below.
                             You have the wrong Monitor , wrong PC or have Video projector that does not match your PC. (there is a cure using adapters)
                             Or even using the wrong DVI cable, not DVI-I on both ends, a.k.a. 24+5 cable dual link.


Adapter choices, problems  horrors and cures, all:
First off
there are 2 top horrors with DVI.  #1 (DVI-d)   missing C1 to C4 pins.(#2  always look for missing pins on the display and the CABLE ends.)
The most hard of all , is DVI hidden pins, the sellers lie about what you bought, and you can't remove the casing to the adapter and you see from outside the 4 pin C1 to 4 are there but inside they are NOT. (DVD-d only it is)
The big lie common is DVI-I and is NOT. (and true for inputs and outputs  of adapters) 
Then DVI-D only monitors.
Then DVI-D only cables.  even single link.
 
My old ViewsonicVA1912vb has no DVI-I jack it is a DVI-d jack only, so all passive analog adapters connected here, fail. This is a digital only DVI port into the monitor.
If Pins C1 to C4 are missing , VGA adaptions will fail on any analog pure source. RGB, the Red /Green/ Blue lines are missing here.
 
VGA
is very fast going Jurassic gone. (but techs still use it for sure just working  BIOS settings or simple tests to find out why a PC is dead or the like... )

The basic pitfalls are here.
  1. Not using active, adapters when you must. ( in either direction  (analog to digital or  digital to analog  ,example: DP  to VGA) (or DVI-D to VGA must be active adapter chip fitted like seen below)
  2. Using very old VGA that is 2 decades old and no modern PC supports the old VESA standard that used 3 wired jumpers back then. (very very old monitors pre year 2000)
  3. Thinking adapters are bi-directional and are NOT  (read the sellers ad. very carefully for direction , PC to Monitor) BiDirectional are close to impossible to design.(lacking a huge switch)
  4. Adapters must honor (passthru)  DDC and eDID chips  or it must supersede it or the PC will think the monitor is missing. This is the Plug and Play chip that is very important.
  5. A VGA adapter the PC VGA must see the  3 resistors (at far end), RGB line terminators of the PC will think the monitor is dead, click above link for why.
  6. VGA and DVI  do not support sound ( see this simple exception)
  7. Active adapters need power to run, some ports, the power pin is dead, (old or cheap PCs can do that , like pin 20 below dead) (VGA has no power pin) DVI is Pin 14 (5v),HDMI  pin 18,+5 V Power ( 50 mA max)
  8. Warning, many sellers of adapters do not even tell you if it is active or passive and many are totally clueless (fleabay toy sellers are daft?)
  9. The below photo, is DP to VGA active adapter, see those chips?, and does not cost $1 far more.( it is not just  wires end to and like in Passive adapters. These 2 photos show what really is inside one.
3 chips, one large is DP to RGB and regulator and crystal clock and EEPROM. This will cost you from $10 and up to $50 (depends on conversion and rarity)
R/G/B means red/green/blue video signal driver,  DDC is the eDID plug and play pass-through. SPI is the serial boot EEPROM yes this chip has a tiny OS running inside it. The eDID is bi-directional see that?
This steals power from PD power pin20, if power is missing on that pin this will be DEAD.

The  DP Power for connector has(3.3 V 500 mA) no lack of power here, so is never a problem unlike weak HDMI below.


Now a harder one, VGA to HDMI  This is a pure ACTIVE Adapter and must have 5vdc power booster, even  a  $1 Dollar Store (tm) Cell phone USB power wall wart works best)
VGA has no power pin, so the below must steal power from the HDMI TV or monitor, and that can fail easy for lack of proper power, that means Amperes to run all chips inside the adapter.
The insides of this device, will have 2 or more chips to do the job. (just like the above DP adapter has) It is anything, but simple.


Adapters are very tricky
:
The lists below are  all left side (source) to right destination monitor.(or TV or Video projectors )
I must say I only get into trouble with devices here that are DVI-D only and the seller selling has no clue it is that. (and marks it DVI-I and is NOT) Same is true for monitors and cables sold. (cheap is DVI-d + Single Link)
 
Modern problems: (examples and why some fail) 
These tests below are only done , using new monitor on old PC or old PC with new (DP) monitor with only one input choice. (or   projectors)
The old VGA is first. (1987 to now) "War Games" old. (like the movie)

VGA to DVI-d (active only works and only rarely done or seen today and needs power supply to do this as all do , analog to digital) This are more aptly named converters.
VGA to any other class digital DP ,HDMI, must be Active rated. (mostly never done but to be complete I add this here.
VGA to DVI-i will be passive if pins C1 to 4 are used but not if pure digital DVI-d  that is active device.
VGA to HDMI(active adapter) (say for an old PC to new TV)
 
DVI: (problems)
Next is DVI: (the harder nut to crack !) < can be... DVI-d only , also knonw as 24+1 and  or called DVD-I = 24+5. (c1-4 + large ground spade)
DVI-I to VGA is only a simple passive wired (DVI-I means does both analog and digital) see these $1 adapters below.
DVI-d  to VGA must have an active chip and needs power to work. (never heard of any DVI-d only video card) this problem only happens when using 2 adapters inline.(or cables DVI-D only)
DVI-A , anything, mostly never happens ever, for sure not video cards.  Missing 12 pins ! seen here.
DVI to HDMI

Next up is modern PCs using DP. (many new PCs only have DP input monitors, or the TV is HDMI only.
DESPLAYPORT(DP)
DP to HDMI works . (A Super common usage from PC to TV) TV means modern HDMI only Televisions.
DP to VGA (digital only to analog only, is an  active adapter) You won't like the resolution choices, but this adapter is good in technicians tool box. (with only some old VGA tiny test monitor to use(portable)
DP to DVI-I  (most are really DVI-d only and sellers never tell you this)   (new PC to old Monitor with DVI only inputs)

Last is HDMI (warning HDMI power pin 18 is limited to just a weak 50mA currents , very little, for sure use booster power pack or USB booster here !)
TVs and PC very common:
HDMI to DP are  rare or super expensive. $20 to $50 (with USB power booster on better ones !!!) Some gaming platforms (like XBOX) have only HDMI out, and you have a DP only monitor. bingo.
HDMI to DVI (    twin pack  ,one for each direction)
HDMI to VGA  sure.(I have one) (mostly technicians tool) but mine has 3.5mm audio side port  (output).

Do not fear doing double adaptations, I found no problems at all ,except DVI-d  (and the seller called it DVD-I and is NOT) cables too.
If fear gets you (sure it can) buy only active adapters (most of the DP and HDMI are)


Next are actual SOLUTIONS: (top) and all seen here I have and tested.

The below $1 solution:
I  have many of these below ( Most times comes free with new monitors and cards) and every one  works perfectly!
These are all Passive adapters. and pins C1 to C4 must be present or it will FAIL. 
Winner #1:
The old tried and true.  DVI-i (passive) to VGA:  (For PCs lacking VGA ports and you  need one if that is all you have on your monitor.)
These do not work backwards,  this is for VGA monitors only (or for   projectors) etc end points.

These DVI-I to VGA adapters Winner #1
These a cheap due to they only have hard wired jumpers inside, no electronics at all , no I.C, chips  at all.

THINGS that make you think the adapter is failing,  but is not. (a side topic related)
Now some other funny rules: Due to Energy Star rules and such.
Most video cards made shut down for this list of reasons. ( all monitors warn you , lost signal , lost sync or going to sleep, if things are wrong)
  • The card can shut down via windows power settings, sleep, hibernate settings ,etc. so disable that in control panel. (or learn how to set windows presentation mode, like when using a protector)
  • The card shuts down if the RGB (VGA,DVI) line terminators are missing for any reasons what so ever (cable missing or bad , bent pins on ends of cable or using the wrong port)
  • The monitor turned off will shut down the GPU card. via 2 ways, terminators are disabled or eDID signals. (Energy star games I call this)
  • Newer GPU  chips, if overheated shuts it self down ,just like all CPU chips have for decades.
  • Most relic monitors 2010 or older have this silly (now) power saver  internal feature, seen inside the  OSD menu,  turn that off , also see timer clock there , on some, turn that off.
  • Always test BIOS screens first to make sure the adapter works before Windows or Linux loads.
  • Always COLD BOOT The PC FIRST, so the BIOS sees the Adapter and end point online. (or it can fail)
  • A new PC (for sure 2020 up) with hard nut, UEFI CLASS 3 rules. locked in CLASS 3.  (I avoid them) but these new PCs will never run old GPU cards, again. (a sad day for any technician)
  • Not doing a hard power reset, as a last resort. (BIOS menu's dead)


HERE IS HOW TO AVOID AN ADAPTER the magical $9 video card.
Or just a Test card , GPU cards
I like to have in my kit to test PCs. (simple and see those 3 ports ?)  USE THIS IF ADAPTERS FAIL or hard to find.

The below are some cards that  are good and make testing easy, (not for gaming ,just for document creation, cruising the Web or testing)
If you have a legacy PC you love, buy a used  GPU card for $10, end the pain if CONVERSION  and ADAPTION. Upgrade the GPU card, there are 1000s of cards, all very cheap now.
One very nice card and cheap is the GFforce 8400GS with 3 ports like this:  VGA.HDMI and DVI-I , a technicians dream card for testing.  3 very common ports.
If you are not a gamer (or like kind intense fast graphics user), this is all you need ! No need for a $300 GPU card unless you really need one !
You'd do this if your monitor has no port matching your PC. )  $10  for  for sure direct connection is best. Tested on W10 -64bit,  v1903. (all ports work)

works with any monitor but DP.(I have 2 of this cards to do testing)


BACK TO ADAPTER EXAMPLES NOW:
One more winner #2, works like a charm,  HDMI to VGA (sold on Ebay) comes with audio output cable 3.5mm for HDMI sound to your sound system.  (active conversion digital to analog VGA)
Again  a technicians dream , and if you only have an old VGA monitor, this will make it work.  (or as I do , have this very old 9" LCD VGA monitor that I tote  around for service work.)
It even works inserted to my wonderful DVI-I to HDMI adapter (2 at once, in line) seen at winner #3 below.
This is an  ACTIVE adapter.(note the sound jack feature, audio line out)
Winner #2   This is the Bee's Knee's ! Cute as a bugs ear?
One more winner #3 same place ebay. (even the above inserted to HDMI  below  works) a working double conversion,  the hard way.(how useful that is)
DVI PC port to HDMI out. DVI is 100% digital.
Winner #3 !  no DVI monitor? Just HDMI  Great for TVs ! works inline with above too!!!
The below is for very new PC, and only very old VGA monitor to test the PC or to a VGA Projector (or whatever VGA) NO DP monitor?
Winner #4,  Modern to Relic conversion.
I also have DP to DVI-d that is very useful and can do DP to VGA or HDMI or DVI.

DVI:

MAX PAIN Back to DVI topic: (no other system of Video DVI causes such pain.)
The pain only comes with running adapters, wrong, or wrong cables or wrong monitor that is DVI-d input only. 
Learn first that most Video GPU cards are #2 below, full blown DVI-I.
The problem is only caused by lies told by cable or adapter makers. (some just are clueless as to what they sell, I call that the fleabay disease)
DVI-I sold is really DVI-d and worse single link.
Look for missing pins, but adapters are sealed up  and the lies are so deap inside you can see that. (if no gold pins seen inside the hole  its missing that pin)
Many times you see #2 below but in fact deep inside , no c1 to4 is present. DVI-d at best.#4.
DVI-d has no analog signals out. RGB is dead. (on purpose)


DVI:
The most common on PCs are #2 (and is best) the Video card  DVI-I dual link #2 is best and runs anything DVI. (this is why it is best and at full bandwidth too)
The problem child's are mostly monitors and projectors and cables too.. (TVs mostly do not have DVI)
The max pain is #3 and #5. (#5 is  chicken lips rare)
#3/4 are Digital only inputs to monitor or cable,  and needs and Active adapter to work.,(analog to digital it must have chips )
#5 is pure  analog RGB input to a monitor  this mostly not in the wild, but works VGA direct or anything else needs active chip to work and power to run it.
#1 is very rare but is just low bandwidth. (but can run anything adapted)
#2 is the best. (just  low single bandwidth) Most video cards dare #2, no better adaptation exists here,  this is prime.  (make sure the cable is same pin count)

The 2nd and 4th down are the most common DVI and 2nd being the most versatile. DUAL LINK is best. This class of port is the most tricky of all. (not #2 below) #2 is best.!
The 5 kinds of DVI, the 3 and 4th down are digital only and if a monitor shows this jack , all passive analog adapters will FAIL.

Pink pins missing means no RGB video lines.
When using dual link, at a refresh rate of 60Hz you can get a resolution of 25601600 and for intense gaming monitors refreshing at 120Hz you can get 19201200.
 Single link: 1920  1200 (WUXGA) @ 60 Hz
DVI-I male (a.k.a 25+4) and is the best cable to own, that way, any adaptor to the monitor has a change of working at all.
To save money most monitors are bundled and packed with the  cheap lame cable #3 above DVI-d single link. (sadly)
Just because you see pin there, does not mean it is wired, and for sure working.

version 2.  8-17-2019  ( the horrors  of adapters are  huge) Hope yours is not.