My Windows Computer Won't Turn on, Why?

Hello,

It definitely sounds like a major component failure, most likely the power supply (PSU) or the motherboard, as previously suggested. Out of curiosity, did you attempt a BIOS update right before this issue occurred?

To isolate and eliminate a potential motherboard or short-circuit issue, you can try the following steps:

Out-of-case test (Breadboarding): Remove the motherboard from the computer case and place it on a non-conductive surface (like the motherboard's cardboard box) with only the bare minimum components installed (CPU, one stick of RAM, and power cables). This will help determine if there is a short circuit or ground conflict with the case.

Jumpstart the motherboard: Disconnect the front panel header cables. Use the tip of a flathead screwdriver to gently bridge the two PWR_SW (Power Switch) pins on the motherboard for a second. If the system boots up, your case's physical power button or its wiring is faulty.

To test the power supply:

The Paperclip Test: Disconnect the 24-pin ATX connector from the motherboard. Use a paperclip to bridge the Green wire (PS-ON) and any Black wire (COM/Ground) on the connector, then plug the PSU into the wall and turn it on. If the fan spins, the PSU is capable of turning on, though keep in mind this doesn't fully guarantee it can handle a load.

If you have a multimeter, using it to check the voltage rails (12V, 5V, 3.3V) on the PSU while jumped, or checking the motherboard's standby power, would be the most accurate and convenient way to diagnose this!