Is my PSU dead, or could it be something else?

[karzons]

I've been using this computer for a couple of years, and after leaving the room and coming back I noticed it was just... off. Thinking maybe my cat pulled a cable loose, I checked the external wires and tried turning it back on. The fans (or at least a fan) just sort of repeatedly revved up partially and back down with no screen response or motherboard beeping so I turned it back off. Cleaned everything, checked the wiring, etc. Now it gets no response from the power switch whatsoever (no fans or devices turn on).

I assume the PSU needs replacing, but the one question mark is from the fact that LED on my PCs memory panel and lower power devices (ie a mobile device charger) connected to the USB ports still work as they always do when it's off/standby. So it's not 100% dead, anyway. Any thoughts?

 

[Burpo]

It is most likely your Power Supply.. Many don't die completely, but lack enough volts to boot.

 

[Harvey]

Visually checking the wires and connectors from the PSU to the motherboard may not be enough. Unplug and reseat all of them to eliminate the possiblity of a faulty connection.

Thinking maybe my cat pulled a cable loose, I checked the external wires and tried turning it back on. The fans (or at least a fan) just sort of repeatedly revved up partially and back down with no screen response or motherboard beeping so I turned it back off.

If the PSU isn't failing, this indicates an electrical short that would cause the PSU's protection circuitry to shut down the system. Unplug and re-insert all plug in devices, including your RAM, vid card and any other plug in cards you may be using.

If it still fails to boot, remove all plug in devices, except your video card and one stick of RAM, and try to boot.

If it still fails, try again with the other stick(s) of RAM, one at a time. If it still fails, borrow a known good stick of RAM from another machine.

If it still fails, try another video card.

If it still fails, borrow another PSU. While you're at it, if possible, try your PSU in another system. You don't have to remove the PSU to try this. You can arrange the other PSU close enough to your machine, or your machine close enough to the other machine to CAREFULLY and SAFELY connect one to the other for a brief test.

This isn't a permanent setup. All you have to do is make sure everything is mechanically stable for this brief test. You can power down immediately once you see that it is beginning the normal startup process, instead of shutting down.

If your PSU works with another machine, the problem may be that the motherboard is shorting out, possibly from a screw head or the surrounding solder pad to the case. The most labor intensive experiment would be to remove the mounting screws holding the motherboard, elevate it slightly and insert an insulator, such as a sheet of plastic or cardboard under it. If the machine then starts to boot, you've found the problem, and you can carefully re-install it.

If a part on the motherboard is fried, unless you're a very good and experienced tech, repairing it may range from difficult to impossible, and in any case, more costly than buying a new motherboard, but at least, you'll know you're buying the right component.