Desktop PC dead and  "Strip Down" testing.           
Or what is a Minimum system?

You are here because, the PC is dead,  the PSU is dead, or runs for 1second and goes dead. (goes silent is dead for sure)
Power button dead, or blinks, its LED lamp acting odd, PC silent all fans dead?  POST codes do not show up and no beep codes..
This is not about dead desktop monitors, .nor about plugging the monitor data cable in to the wrong port (VGA, DVI, DP, HDMI)  if you have GPU card us only its PORTS.
This page is not how to fix NO BOOTS, but is about DEAD PC's.  (no boot is simple, the boot order is wrong, or HDD bad or corrupted) Boot order wrong can be a bad RTC coin cell battery .

All PC's do this if you keep it for 10 years or more, even less years if it  runs too hot and a real long time (hours used and for sure in a hot room)
The Macro list is simple:
  • PC needs the a new RTC coin cell battery, POST errors on Dell are 123x  (and xx3x)  they last 5-7 years so replace per your free manual.
  • PSU is overloaded (see 14 tests below to find why) {a.k..a shorted RAILS, and modules shorted, the PSU will  not operate } By DESIGN. (this is the no fire and smoke deal)
  • PSU is bad.(see bench tests here)
  • Or simply need the long hard RESET done.  HARD RESET. ( this cures ESD, Latchup and failing Sleep modes, the latter is only temporary due to bad drivers on the PC)

Evidence seen or not or heard or not. (screen dead or errors on sceen or silent PC or not)
POST code errors, power on self test errors. LED codes BEEP codes or both are clear as day hard evidence. beep codes or LED status codes
The CD tray must eject with the button next to it now. (if not ?, power is dead)
Case lid removed, the center of the motherboard,  LED going tells you at least standby power is good. (if  not glowing PSU may be dead or no AC power to it)
If just the screen is dead and fans spin test the monitor on a 2nd PC next, and then make sure you are using the the correct GPU graphic port ,some PCs have 2 ports DP , main offline and GPU card DP only works now.
DP means display port, the video cable must be plugged into the GPU card if one is present.  (card means PCI-e expansion slot cards)

    Fault isolation tests or reducing the PC to a minimum system! aka, the strip down test  or removing all shorts.
    The minimum is one each of ( MOBO, PSU, 1 DDR RAM stick , CPU)   do not pull the CPU as 99% of NOOBs wreck the socket pins NOW. (kiss off MOBO if you did)
    The goal is getting the BIOS screens working first. 

    • Pull all USB devices now, they can short.
    • Then open the PC lid left side in most cases (yes, pun)
    • We remove all PCI-express cards from all slots , even the GPU  card  now)

    If the PC wakes up now, you found your short, so replace the part that is shorted, (easy no?) wakes up can mean BIOS screens start working and is goal #1.
    Wake up can mean also CPU fan starts working, or other prime evidence of live.

    Most Desktops are super easy to Diagnose in this ordered list:   this is the LONG PLAY VERSION,  learn that what will be, will be.
    PC's have shared resources if one thing shorts all things on the resource are now dead. (and the whole PC now dead)
    AGAIN 1 more time the RTC coin cell battery not Dead, (below 2.9vdc is BAD) buy one or use  a voltmeter to test it. (your call, but is a show stopper #1)
    1. Do the long power reset first. (this cures , stuck in sleep mode, or ESD latch up events)  HARD RESET.
    2. Remove all USB port devices next.  (unplug the monitor data cables (VGA ,DVI,HDMI,DP) just in  case the cable (etc) is shorted, (some of these have power pins)
    3. Best in all cases all years PC is to pull all cables outside CASE except the 1 AC power cable, make sure AC cable is fully seated at  both ends, even reSEAT it.( use  AC wall power now and not power strips AC)
    4. Open the left side case cover, make sure all power cables from PSU to MOBO are not fallen off or loose, even re-seat them (4 pin yellow wired, and huge 24pin plug) do so only with AC plug unplugged.
    5. Make sure the power button cable did not fall off. (mobo) (mobo = motherboard slang)
    6. Remove all HDD/SSD drives  and all optical drive cables (CD or DVD etc) (If PC turns  on now, bingo for shorted out drives)
    7. Remove all PCI-express socket  cards like:  GPU, SATA, RAID, WIFI, ETHERNET, remove them, all. now. (if found)
    8. Remove all RAM, but one stick of DDR. (most PCs have at least 2 slots some 4 some 6) and test DDR sticks one by one in Bank 0 slot (your manual covers 1 stick usage for YOUR mobo)
    9. One other test is to remove all DDR RAM and hear the PC beep codes, gross RAM failure or blink codes flashed out the same. (see if there is some kind of intelligence only here, as opposed to 100% dead silent PC)
    10. The CPU in almost all cases never fails, but if the heat sink fell off or the TIM thermal compound is bad it can overheat in 15 seconds and self turn the PC off. (Intel Inside did that magic at 90C overheated)
    11. My new Motherboard has two M.2 NVME gum stick drive cards,  that can short, so out those come  now (1 screw). some MOBO have M.2 WIFI card here, remove that now.
    12. If  you get this far and PC is still dead the PSU is bad.. (the PSU can be $50 the MOBO $300 a no brainer, econ101 decision. (but gee all shops have  spare 700w PSU waiting on the shelf)
    13. If the new PSU fails the mobo board is bad. (most times inside it are bad CAP.'S ,but we think this ended in 2007) but gee this happens too.
    14. If your current PSU fails bench testing,then it is  bad,  ( if the mobo is shorted) many did during the CAP Plague. over 13 years ago.
    (factoid #1) SOME PCs, have a PSU that the fan is dead and silent (by design) if below 20% load, or is running nice and cool. (so focus on CPU fan for power death)

    Last always last is to blame the failure on the motherboard.  (some can cost $300, and new PSU is tried now. (do the PSU bench tests at # 14.)
    If the new PSU is still dead?, the mobo is history.
    A MOBO fail mostly for 2 reasons, lightening damage (hits) or ESD hits bad CAPS,  or user abuse and #1 on the list of abuse is hotswapping any device or connector inside any PC.

    What is a minimum system?  REAL EXAMPLES and fully exposed to see what is going on here.
    NOT saying to do this, only that the PC case is optional, one can bench test it all for sure. ( see my Dell 790 test bed here)
    You can remove all SATA devices, HDD, SSD, M.2, DVD drives all drives removed and BIOS works (like the Dell F2 key or HP Esc key works.)
     Power on any PC and quickly Hammer (geeks call it spamming) the BIOS key. (on Dell its F2, ESC for HP) F2 F2 F2 bingo BIOS POPS.
    You can remove all RAM, but 1 stick in bank 0 and run as a single channel RAM bank sure can and test them 1 by 1 that way.
    Most PC today (except below PC) needs no cards in the PCI-express slots,  at all, even the GPU card, is removed and the on board, VGA port used, after a full reset.
    Remove all PCI-e cards of any kind if PC has CORE i3 up, generation 1 Nehalem and up processor you need NO PCIe GPU at all.!
    Remove all cables but 5 , AC power and the keyboard seen below and the VGA port to my VGA screen.  (and 2 DC power cables seen below, 24pin and 4pin VRM power.)
    On DELL PCs it will complain big time for other jacks unplugged,  the front panel jack not there, and other, just ignore that, and get BIOS screens working first. (a goal #1 is BIOS)
    Only use a known, good monitor LED, no monitor 2009 and older should be used there are dead or intermittant now, all are that old due to CCLF lamp death.

    This photo below shows all (most) things missing and if still failing the GPU card is removed next, (we have and use old $5 GPU cards to test any PC, with SECURE/SAFE UEFI BOOT is OFF)
    XW4600 HP workstation MOBO:   I'm booted to USB stick  demo live Windows 7 PE media, for testing there is no HDD here booted, one can use Linux DEMO mode  to do the same thing,

    Warning:  no two mobo made have the same  power pin out for the below connections front panel , there is no ATX spec standards  on these pins !  (READ YOUR PC MANUAL)
    These 2 power on pins are marked as , 1 is ground other is "power on" pin logic input, and is easy to jumper (momentary) The power panel or power button here is missing.
    RTM read your manual  find the 2 pins and jump it momentarily. example HP  (pin 6/8)
    HP Z600  Power on Pins P5 Jack is not in the HP manual, so is secret, until you look and see pins 16/17 or reverse engineer it.
    Here is one more example of jumping my Dell 3020 (pin 3 jumped to 6)
    The Dell 790 pin out is here.
    My Dell 380 is covered here for the odd power on method,  (I/O panel only switch)

    Top and great  makers of mobo  , covers this topic of front panel wiring, ASUS, MSI, GIGABYTE 

    My Asus Z720-prime manual shows (Page 1-21) These pins clear as day. labeled PWR and GND.
    Asus makes DIY mobo, and with great documents. (better than most makers if not all)
    OEM PC makers do not, and do not document connectors. (all the non ATX connectors not covered, they will tell you just plug it in and not to worry)
    The magic full power hard  reset can in fact wake up a dead motherboard.

    This one page is to help you get at least one BIOS working , and may take a new PSU.

    My 790 Test bed PC, is naked as can be. benched. (running Furmark 3D APP) NO GPU card here, and we can  test with 1 RAM DDR stick to.  The extra fan is to keep South Bridge cooler.
    The CPU fan is never dead. It must spin and on the Dells F2 key most get you BIOS main screen.

    LAPTOP (LT) power structures are complex.  (the actual PSU is hidden deep deep inside all LT) 
    Here is a page I made on Laptop power isolation testing.

    The fake Desktops  , AIO all in One can be diagnosed just like laptops. (skip the huge battery topic)

    Some facts about PCs.  ORDER, PCs BOOT in a serial order.;  (basic basics 101 PC)
    • Power on can fail, this is first, no power no joy ever. (call power failure) The hard power reset can cure this.
    • BIOS is dead, (fails to post some say) one more symptom of power problems (shorts)
    • BIOS works but the POST locks up mid scan (rare but I have dual GPU card, that will never run on some PCs , causes a DELL to lock up mid POST scans)
    • If you get this far you may get POST errors now, with beep codes or LED codes.
    • Last NO BOOT, at the end of the POST , the PC uses its BIOS boot order to boot things, if all things in the list are dead, there will be not OS BOOTING ever.

    version 1.  12-12-2018   v2, 12-1-2019