In most cases, a truly dead PC is in fact a hardware failure and never software.
In fact the goal now shifts, (forget Windows/Linux OS) we shift our goal now to getting BIOS screens working (or super modern UEFI screens) BIOS is firmware and does not self erase or forget for 100 years. ok?
I will do this for all PCs , Real Desktops and mobile PCs (on newer Laptop/notebooks, the makers moved the main battery deep in side and is super thin, and needs the bottom of PC removed first to remove it)
This is an ordered list:
First make sure the AC power jack has power , use desklamp to test any outlet. (or
Your room has AC power ? If not service panel breakers are tripped. (do not use power strips now for testing, use direct wall AC power for power to this dead PC)
The AC power is connected to your PC. (do not use the large batteries on laptops , remove this battery now,;we are diagnosing a DEAD PC and AC power good) (Re-Seat the power cords now)
You push the power on button and... (on a Laptop, one can spill drinks on the power on button and it fails , or just wears out, if you hold finger there and wiggle it and power goes on the button is END OF LIFE)
If the fans all spin and blow air and PC does not overheat, then it is not totally dead. (sure the OS "Operating System" can be dead , we can install w10 this way)
My desktop has 3 fans and all 3 must spin, or it will fail. (Laptops mostly have 1 fan and it must do its job or it will fail) My PC GPU card has fan too.(or this video card overheats)
Desktops have 2 fans (CPU and PSU) at least, that must spin and blow air (heard, seen and felt) yes we use 3 senses to prove this out. (as in seen not to stall fan or packed in lint) Click overheat above, to see why.
Next is beeps and blink code errors, CAPS lock key blink/flash codes, write them down first, (flash flash flash, pause ,repeats) then look it up in your service manual. (relic PCs beeped but not now the flash LED codes)
Better PCs also send text to the screen called P.O.S.T error codes,( Power on self test ) Some desktops by HP and DELL have 4 LED POST error LED panel on the rear showing POST codes too.
Read your serfvice manuals, this is covered on top branded PCs.
The screen dead ?, but PC seems to have power is here. (fans work).
BIOS Screens are next:
If you PC is 7 years old or greater the RTC tiny coin cell battery can be dead.(or weak) and BIOS WILL GO nuts as will time of day and date , as seen on the BIOS screens.
The maker of the PC will pop up a graphic ICON like this below, if you see this or text of any kind the PC is not really dead, at all, only the OS (Windows is dead)
As you can see this PC is not dead, because fans work and BIOS screens all work perfectly (each maker of PC uses different screens and different hot key to get to all screens of BIOS)
This screen (boot) is a BIOS FIRMWARE message, The "ESC key" works on HP only, other PC prompt with different hot key.
The HP you power on , hammer key ESC, then hit F1 key for the HP information page.
The next thing to do if you see the BIOS screens work is to do a Operating system (OS) full recovery or startup repair, as covered fully at microsoft.com (or do as you OEM PC maker tells you in there service manual)
If the PC is not dead and BIOS works then reload the OS.
On my PC the HP F11 key, is the magic recovery key for Windows full day 1 recovery, this key F11 is different on other PCs. This topic is covered in your PCs service or users manual, read the chapter on RECOVERY.
If you are locked out of the BIOS with BIOS Passwords set, the cure is here.(or far worse bitlocker)
The below covers what to do if the BIOS screens are dead.
No text and no logo?, See causes of dead monitors or screens here.
If the PC is silent that is a true dead PC, and will not have screen messages of any kind.
In most cases, but not all the PSU is defective.
All PC's have a PSU, the Laptop has 2, (1 battery and 1 AC pack with on-board VREGS aka: VRM) VRM means voltage regulator modules.
If the PSU tests ok, by itself then the motherboard, is bad (unlikely) and for sure the motherboard has what I call power overloads.
Overloads are shorts, there are 4 classic Van Neumann ways to short , (DC power rails, data bus, Address bus and control bus)
To find who (what) is shorted we do what is called computer module Isolation testing, ( simple pulls)
There is no order here, we pull that which is the most easy to pull first. (USB is first, things connected...)
Pulling RAM (DDR) all out and putting 1 back in and testing with only 1 RAM stick at time is a common practice on all DEAD PCs.
Other odd failures, the power switch fell off the mother board power pins. (oops) (in laptop this can be a ribbon cable loose)
Uses a cheap voltmeter (sold at Walmart for $20) to measure power rails or the power pack output voltage (19vdc?)
The Laptop AC power pack on mine is 19 vdc output, if it reads 0v it is dead if it reads 5vdc it is dead , or the wrong pack (watts or volts) or the laptop has shorts inside, even the main battery shorted.
The power jack on side all laptops can break, if you see damage there, well it is bad. Repair all things seen bad. (laptops love to fail this way) Some have this and are easy to replace if bad.
The PSU in all Desktops (real) can be bench tested, using just a paper clip, to test it seen here, check and see if any PSU is defective.
See that motherboard, see all those things connected to it, pull the HDD now (cables on Desktop) PULL that CD/DVD/BR DRIVE. (optical drive.)
The PC can also have other things to pull, SD card readers, PCI-express cards and more, pull them all and see if the PC wakes up. (do not pull the 24 pin power cable during overload testing)
(one Laptop has shorted Dialup land line modem inside shorted, and is useless today, so out it came PC now runs)
I cover all Isolation (pull) tests here, in the PSU page.
The PC IS NOW NOT DEAD: (next is booting)
HDD testing is next the BIOS screens all work so next we test the HDD. (hard disks drive)
The boot screen that works, I can go in to any BIOS screens and see all things normally, but say the PC will not boot HDD-0 (SSD-0)
I then go to the BIOS Boot screen tab, and see if HDD 0 is listed and at top #1 boot order.
If say your BIOS screens can not see your boot disk present (plug and play ID) then the HDD is dead.
If the HDD 0 is missing in the BIOS BOOT DEVICE list, most times the HDD is dead. (if it makes no sound ear held close to it, then it sure is dead)
If the hard drive does not spin , it will not show up in the BIOS boot order list. (that is because the plug and play (PnP) identification is dead now ,due to a brick dead HDD)
Some bad drives, spin but PnP ID fails and BIOS can not see this dead drive.
If the drive shows up and will not boot and OS, clean. The next test saves you lots of time.
We test the HDD first and never just reload or upgrade any OS with out doing HDD tests first (SMART tests using boot DVD or boot USB stick)
Some BIOS has HDD drive test page (it is rudimenatry test but if fails the drive is bad)
My HP F9 key (power on hot key) if the HDD is missing the drive is dead.
If the drive is good, and SMART tests pass muster, then boot order is next.
See the order now. (some rare and cheap PCs this order is fixed forever)
HDD BOOT ORDER: (each BIOS looks different here)
Some just show HDD0 , others will even (nice) show the PnP ID message truncated (shortened)
Note the below shows the Matsushita drive. Best is to look at your HDD, read its label and know what you have. (Seagate, WD, Toshiba, HGST or my M.2 by Samsung)
2010 HP laptop Elitebook Below. With my Linux boot USB present. (my Laptop has 2, SSD drives now, one is in place of DVD drive using a caddy seen as upgrade bay here)
Old legacy PCs . (if I remember that long ago?, the word "Hard Disk" , will be missing , if the drive is dead) This BIOS is dumb, it does not share, PnP data with the users, for far better ID.
Now last and best of all for any person working on PC's (I boot to windows demo disks WIN PE)
Run HWinfo32.exe (portable) free, of charge to use. (and for sure malware free, virustotal.com, clean) The below is my z270prime with 2 HDD and 2 SSD M.2 cards.
As you can see you don't need to remove the HDD to read the label on top at all.
I booted to my USB Windows 7, PE boot demo disk and run this program. (app) looking for dead drives. None are dead.
Last of all , the most cheap PCs of all , and not enterprise grade ( HP Zbook are best and G2 best of all...) , many have a FIXED BIOS, in that you can't change squat.
(it is frozen to HDD0 boot for ever, so if the HDD fails the BIOS just opens up this dumb BIOS screen and freezes after all it is too dumb to do any thing else, but some do beep codes for dead HDD )
YBMY, your BIOS may vary , actually they ALL DO.
version 1. 10-10-2018