A couple of months ago I stashed my old computer into the basement. Now I wanted to "resurrect" it. Problem is, it doesn't want to.

When I plugged in the power cord without having anything else attached to it, the computer started, I could also hear the hard disk and all that. I wanted it turned off until I was finished so I pulled the power cord back out. After that it was dead.

When I turn it on now, both the PSU and the CPU fan start to rotate, but this is all that happens. The hard disk doesn't start, the monitor gets no signal, etc. USB devices still get power, and I checked the hard disk and CD-ROM power cords and they work, too. So the PSU is probably fine.
First I thought it was the video card, so I bought a new one but nothing changed. Now I know it must either be the CPU or the mainboard. How can I find out which one it is? When I leave the computer running for a few minutes, pull the cord and remove the CPU fan, the CPU is completely cold. Does that mean it's dead? Or can that be caused by the mainboard, too?

I know these things can't really be determined without trying the individual pieces of hardware in other systems, but I don't have that option. The only option I have left is replacing on of the 2 components, but that could become real pricey....

TIA

Was every connected to the computer like mouse and keyboard and monitor ?
Because one of the option in the BIOS setup is stop at any Error .
Missing above hardware is such a error.
If everything is connected than it might be possible that CPU is the problem
Same happens to me with my old computer also when I stop using it after buying a new one.

Yeah I sometimes connected everything when testing, but my computer used to start without anything attached to it. Except the power cord, of course. And I've taken out all the hardware and the different RAM chips... nothing helps. Is there any way to test if a CPU is dead without using a mainboard?

Sometimes a bad clock battery also prevents a startup (although Macs are the most notorious for this 'feature'). It could still be a PSU fault; do you have another power supply you can borrow from another computer? Also check those power connectors, especially if the computer is new enough and has an Intel chip that requires an extra high-current supply line in addition to the usual ATX connector on the MoBo.

AFAIK, alive motherboard should beep on startup. If there is no keyboard, videocard, harddrive, or there is a problem with memory, it will beep (different beeps means different system status - search for bios beep codes somewhere). I don't remember if it does this without CPU (or with broken CPU) or not, but I suspect it does.
So no beeps means motherboard is dead. This is 50/50 suggestion, because I'm programmer, not a hardware-inclined person.

Also, check your PSU, try to replace it. Broken PSU (yes, even with rotating fans) may produce similar situation. (Fans rotate, but it doesn't work, no beeps). This happened to me several times.

Reseat all connections and memory to be sure nothing is loose.

Ok, there are no beeps at all. And the mainboard used to beep a helluva lot

I've measured the voltages in the PSU connectors. They're almost as they should be, but I had 14V where I should've had 12V. Could that be a problem? I'll see if I can get a replacement PSU, but I don't think so..

The BIOS battery shows about 3.4V which I'm sure is enough, so it can't be that..

How you did measured the voltage with a device connected or not ?
The battery did you test with battery tester ?
By a power full power supply it does not matter , if not the voltage drops when a device is connected the differences is about 10%

I measured them without any devices connected. So I guess they're correct. I tested both the connectors and the battery with a multimeter.

If you're sure you've checked everything else (and you do have 5v on the supply while it's on) then you probably have a fried CPU. You can pull the CPU out of the ZIF socket (or BGA socket - whatever it has) and look at the state of the heat transfer compound - if it's all dry and powdery then it's not doing its job and the CPU may have overheated.

Before yesterday I hadn't taken the CPU out of its socket for about 5 years. Do you think starting a computer after not using it for three months can lead to an overheated CPU? The heat transfer compound looks alright (it's still liquid) and the CPU does, too...

i find it always helps to have a second machine in case this happens, check the capacitors on the board... if it hasnt been used in a while they can pop, check the tops, if theyre bulging or look rusted its possible one of them has gone.

If the heatsink compound on the CPU still looks good, then it's probably not an overheated CPU. It could be a damaged CPU, but that's very unlikely; it is far more probable that you have a bad PSU. The best way to check is to borrow a PSU from another machine. All other components (CPU, MoBo) are far more reliable than the PSU, although as someone else pointed out, bad capacitors on a MoBo can also be a problem. It is highly unlikely that just the right electronic component failed and cause the MoBo not to beep and CPU not to run; the PSU is really the usual (but not always) problem. The only other common problem I've seen on old boards is damaged (corroded) tracks and RAM connectors.

I'm pretty sure the capacitors are alright.. think I'm really gonna have to get another PSU. Too bad I've got nothing but laptops in the house lately

I've uploaded some pics, though I don't think they're gonna be of any help:

http://www.pulse-soft.com/stash/0809...r/overview.jpg

With CPU fan and heatsink removed:

http://www.pulse-soft.com/stash/0809...ut_cpu_fan.jpg
http://www.pulse-soft.com/stash/0809...an_and_cpu.jpg

CPU from both sides:

http://www.pulse-soft.com/stash/0809.../cpu_front.jpg
http://www.pulse-soft.com/stash/0809...r/cpu_back.jpg

I also removed the mainboard chip heatsink:

http://www.pulse-soft.com/stash/0809...board_chip.jpg
http://www.pulse-soft.com/stash/0809...d_heatsink.jpg

Does anything in these pictures look like it could be damaged?

I've never been able to "see" damage except in the case of bad caps or a fried PSU. The PSU I was able to smell better than see.

My guess is PSU that will only set you back $25 or so. Next guess would be Mobo. Last would be CPU. I once had a system that I replaced the PSU and the mobo was damaged in such a way that it fried the new PSU. So I had to end up replacing the mobo and PSU. CPU was still good.

You may be able to take the PSU to a local mom/pop computer store and have them put a tester on it?