My PC , monitor or TV screen is dead.        

The video ports are called also jacks  "VGA/HDMI/DVI/DP" for PCs , external monitor displays  or even a  TV only.   (mostly HDMI on TV)
A PC can be tested on any monitor or to the TV using HDMI. (or with adapters)
I will not cover 20 year old or older CRT monitors ever again .

In all cases a monitor can be tested on a 2nd PC, to see if it really is dead and not the PC dead, or in the same vein test the PC on  a TV HDMI connected. 
Do I need to say the cable maybe  bad or both ends  the pins bent?  (cables do fail) but fails too on 2nd PC.
In all cases (no pun) the screen must not be cracked like this. (physical  damage is first to find)
All monitors have and OSD menu button that if is dead, the monitor is dead.
If the monitor shows no signal errors be sure to set the monitor the the correct  port (VGA/DVI/DP/HMDI ) the one connected to the PC. Some monitors the port AUTO PORT mode fails, so force it to yours !
If the monitor shows out of range errors that means the PC is set to too high of resolution, (the cure is simple decrease that at the PC, try safe mode to do that...?)
The first test I do (after above is the magical flash light test (UK torch) old pre 2010 monitors and Laptop screens had crummy CCLF black lamps that failed in 5 short years failing like this view below.
this should be clear here what I am doing , right? LCD ok, backlamps NOT OK.
The same test works on TV's. for the same reasons,  BINGO bad BACK LAMPS.
A PC may have 6 GPU ports, mine does,  2 on base board and 4 on my super fancy GPU card, and that means the monitor or TV must be connected to GPU card if present and not the other baseboard iGPU ports.
My page here is not for fixing bad PCs ever see here for that., we know the monitor external fails on 2 PC's.
This Page diagnoses all screen failures, of any type and we will not take the monitor apart, but I will show parts that fail common. (you are on your own inside any monitor or Laptop as they are all very different inside.
I will cover Laptop screen problems later on this page but not now.
DP and worse HDMI oddities:
Some cables or some Displays do not allow hot swapping  the monitor, the cure is simple turn off PC, leave monitor on and power up the PC and it plugs and plays and works.
If running PC with no display at all called Dead heading or headless server cheap, we must use a dummy port connector or the GPU card goes offline, and remote access too.

I will not cover PC stuck in sleep mode or dead GPU cards here.  That is PC problem not the screen or monitors fault. (turn off sleep in the PC) PCs fail sleep if the drivers in the PC are wrong (or missing)
All monitor self sleep disconnected from PC or the PC is dead, all do. (by law)

(The On Screen Display) OSD,    MONITORS only , never laptops or TV. (which I cover later)
This is only seen on actual monitors for 20+ years.
This must work or the monitor is dead, even with no GPU video cable this works.!@@!
Power on the monitor only and push the button on the monitor marked MENU  quickly under 15seconds, if you are too slow , repeat this from power off.
If this fails ,do the flash light test above next. (using same rules of testing) Play with brightness sure., and this 2005 monitor need to have Time out set to max and all things blow marked off to off.
OSD 1, On screen Display. PC is working 100% here.
No SIGNAL or no connections , errors mean PC is dead or  cable bad or not connected to running PC.

  No signal means the PC is not sending signals to the monitor , then goes to black screen. (sleeping)

CCFL lamps go yellow , with white pages.  bad lamps for sure.
CCFL secrets the manual for the monitor or laptop pre 2010 shows these words it is CCFL (toxic, mercury, hg. ) then it is CCFL Hg is the atomic symbol for mercury.
Or look inside for the HV cables and or inverter. 600vdc warnings.
CCFL failure modes all are known,  Dead, intermittent, strobes, or fails hot or cold only, or yellow above.

Monitors stand alone tests, with no  PC connected, no VGA, no DVI no HTML cables attached, example HP LE2002x .
Also learn that many newer monitors not connected to a PC go in to automatic self test mode,  let it and watch what it does, for sure when new to learn this and what it looks like.
You power on the monitor and it  shows, this or the monitor is dead.  The red words below show scanning port that shows no signal. All 100 % normal. for 2 dead or missing cables (this photo is missing cables x2)
   This shows and times out, and then sleeps.(by self)
HP OSD MAIN menu, what you see after pushing the menu button.

If the PC runs you can get there via OSD menu button and crank up the brightness, some displays have dedicated buttons for just that.
Some displays have  built in test pattern , nice to see if the colors are looking ok.
Old monitors have this old school malarkey, timers and what not. Turn it off and then only use the PC side for sleep mode. (if at all) Not Energy Star but Energy-DERP.
WARNING if you do the factory reset seen in main above, all this timer junk goes active, again.(pain)
This below are relic monitors, all this odd timer jive is gone now. forever.  and a Pain if on.

The below should clear, that you need to turn off the stinking rotten SLEEP timer here this be first to check. 2001 to 2010 super common to see this.
I am pressing the monitor bezel Menu button key, now: This is called OSD< for on screen display. (the monitors brain does this , never the PC)
Modern monitors do not have arrow 2 or 3 , no monitor only sleep timers today.
Just turn it off. 3 click here.

If the menu button goes dead, hold menu buttion for 10 seconds and it unlocks it (lock mode off).

More show and tell time.  (hardware) For the curious  only or really want to know.
This is how the guts of a monitor work in block diagram form,  the only major changes are CCFL lamps are now LED starting in 2010 year.

Besides higher resolution and other new features, I offer this as an example of what causes hard failures of  monitors. CCFL wins that award at even 5 years old and now DEAD.

Tubes fail 9 out of 10 times but so can Inverters.
CCFL inverters as seen in monitors or Laptops , 600vdc output, do not touch when turned on.

Actual CCFL tubes in an old monitor 2005,  on newer thinner screens these are all buried deep inside a large glued up LCD sandwitch,  and impossible to remove  and only whole new LCD panel is the cure (we look first not guess)
In the year 2010 all LCD switched to LED back lamps from  large screen to small screens in that order.(history)

LED modern TV , monitors and Laptops too can fail too.  (cheaper grade devices do) Never seen LG fail. or Viewsonic, modern LED fail, me.
This next photo is old CCFL monitor and the two 600vdc jacks seen on the left and the CAUTION word (do not touch me)  do not touch any of this with AC connected to the wall AC jack of any kind.

Laptop comments:
The laptop can get tested with the flash light trick seen top of this page.
The laptops can be tested with an external monitor (using VGA or DP  are common)
Laptops older than 2010 love to fail for CCFL death as most have now  10 years later.
The screens with CCFL most can not be replaced, due to the thin nature of laptops worse every year.
Here I am putting in a CCFL to LED upgraded LCD. ( a gift to a friend this....)

TV, a.k.a Televisions, modern.
These same tests and causes of failure  are the same, only more types of back lamps exist even super hot, halogen lamps.
The flash light test still wins for test #1 if the TV seems to  turn on,  hand clicker batteries not dead.
The hard part of TV is there are 2 screen modes,  TUNER mode and Smart screens, but if the screen is dead you cannot try them easy, only blind with the clicker.
The TV has a service manual that if bought allows you to check all power supply voltages first with a meter.
The backlamp power  pins need to be check of the flash light test show any kind of data on the LCD actual front of screen.
The blacklamps all have a power supply. (not dead)
Most clickers have button called INPUT select and is a good first thing to do just after button "ON" That you  fully know what the input screens look like, on mine over 6 choices, of inputs HDMI and tuner (antenna)
That is all I will say on TVs.  (the service manual is a prime goal on any TV) lacking which , only Gue$$ing works.

Buy LG or SAMSUNG TVs not off brand cheap TV's/.

As you can see there are lots of Video or graphic  ports/jacks. for 3 full decades now.  (VGA is now going byebye forever) Most new PCs may have 2 ports, DP and HDMI, (HDMI for TV is still popular)
DP is best for sure running 2 or more displays.
One can buy adapters from one type to the next.
JACKS so many JACKs (connectors all standard)

version3.  12-9-2017  (12-1-2020) trimmed it down but lots of examples.