My computer won’t turn on.

·	Maybe the parts aren’t compatible, or are of bad quality, or not suitable to the system somehow
o	Power supply stuff
§	Scummy-quality power supplies
§	Insufficiently-powerful power supplies
§	Board needs an ATX12V cable but the PSU doesn’t have it
o	CPU that the motherboard doesn’t support
o	CPU that the motherboard will support, but only with a BIOS update
o	RAM that is not correct for the motherboard and/or CPU
§	Wrong speed
§	Wrong type
·	Registered/unbuffered
·	High-density modules in older motherboards
§	Faulty or flaky RAM
§	RAM that requires a voltage the mobo won’t supply (eg 2.6-volt DDR400 in boards that don’t do voltage adjustments)

·	Maybe the parts are compatible, but incorrectly assembled
o	Heatsink stuff
§	Backwards heatsink or clip (Socket A)
§	Heatsink riding up on solid end of socket (SocketA Thermalright & others)
§	No thermal compound
§	Forgot to take plastic slip off of thermal patch
§	…U mean teh heatsink isn’t optional?  :o
§	Heatsink fan not plugged in, or does not give RPM signal some boards require for POST (Soyo especially)
o	Power stuff
§	ATX12V cable not plugged in
§	Power supply is set for the wrong input voltage (115V / 230V)
§	Case’s Power button is wired to the wrong pins on the mobo (the Power LED pins are sometimes mistaken for Power Button, or silk-screened markings are incorrect or confsuing)
o	Motherboard stuff
§	EMI springs on the rear I/O shield are getting into the USB or network jacks
§	There’s a standoff under the motherboard where it’s not designed to need one, and it’s shorting something out
§	…U mean teh board needs teh standoffs under it?!  :o
§	Case’s front USB ports were plugged in, but the case’s pinout doesn’t match the board’s pinout
§	Stray screw under/on top of the board is shorting it out
§	Motherboard’s chassis-intrusion header is uncapped
o	Drives, cards, add-in stuff
§	CPU isn’t seated in its socket all the way
§	AGP or PCI card is not fully inserted
§	Floppy cable is upside down
§	Forgot auxiliary power cable for high-end video card
§	RAM isn’t seated
§	IDE or floppy cable isn’t fully seated
§	Forgot to plug the power cables into the drives
§	Keyboard &/or mouse plugged into incorrect PS/2 port

·	Maybe the parts are compatible and correctly assembled, but incorrectly configured
o	Motherboard stuff
§	Clear CMOS jumper is in the “clear” position
§	FSB and/or memory jumpers are set for an unworkable speed
§	Onboard video has failed to transfer over to an add-in AGP or PCI video card
o	Drives jumpered in conflict (two masters or slaves)
o	IRQ conflict between PCI devices

·	If the parts are definitely compatible, correctly assembled and configured, but still won’t work…  maybe something’s faulty?
o	Narrowing down the list of suspects
§	Start by unplugging drives from power & data cables, test core components (mobo, PSU, CPU, video and RAM) in the case
§	If necessary, benchtest core components outside case on cardboard
§	If no joy, use a compatible known-working system to verify whether video card and RAM work
§	Consider doing likewise for the CPU, PSU and mobo if practical & safe to do so
o	Taking action once the list is as narrowed down as practical
§	If you have known-working substitute parts from another system, try swapping them into your core benchtest setup (eg, known-working & compatible CPU, RAM, video card and PSU would narrow it down to just the motherboard itself being good/bad/misconfigured)
§	If you have to buy something to continue testing, and your PSU is a high-quality one, pick something else first.
If you have to buy something to continue testing, and your PSU is a low-quality or skimpy one, listen to the little voice and use this as justification for a high-quality one with plenty of wattage.
o	Understanding & interpreting the symptoms in the core-components scenario
§	Motherboard starts, runs, & turns itself off after a little bit
·	Motherboards will shut down if they think the Power button is being held down continuously for ~6 seconds (a faulty Power switch on the chassis could be the problem)
·	CPUs will order the motherboard to shut down if they’re overheating
·	Some motherboards won’t stay powered on if they aren’t seeing an RPM signal on the CPU FAN header (Soyo especially, overridable in BIOS)
§	System simply lies there and ignores me with its green LED lighted, showing it has power, but no dice when I press the Power button
·	The motherboard is waiting to see an electrical connection between the two pins that the case’s power button is supposed to be plugged into.
§	System’s “power-on” LED is lighted at first, but it goes out when I try to power up
·	PSUs will trip their internal circuit-breaker in dire circumstances (defect, overload, short-circuit condition)
§	System emits one or more beep codes, or its onboard speech thingie gripes about “System CPU Fail!” or whatever, or its LED diagnostic thing shows an error code
·	It’s trying to tell you something.  Look up the error codes in the manual or at the manufacturer’s site.  Use the diagnostic info to focus your efforts on what seems to be the indicated problem, but realize the diagnostics can be incorrect about what the problem is.
§	System fires up its fans and stays running, but that’s all that I get, and I verified as many parts as I could, and used the known-working parts here.
·	Something’s not compatible or suitable, or
·	Something’s not installed right, or
·	Something’s not configured right, or
·	One of the parts is faulty