I think I have a bad power supply on one of my computers. I'm wondering what you guys think. I have an old IBM Thinkcentre, I press the power button and it lights up, I see the processor fan and the power supply fan start to turn then stop, and nothing comes up on the screen. I hear no beeps or sounds at all.

Marc...

What happens when you press and HOLD the power button in ?

Kev

If it is off when I hold the button the light comes, the power supply fan and the processor fan starts to turn for a couple of seconds the stops. If the light is on when I hold the button the light goes off and nothing else happens.

It sounds like the motherboard to me.

http://www.techrepublic.com/article/power-supply-troubleshooting-with-a-multimeter/1056686

A PSU is cheap...or pull another out of a spare machine..got a buddy that has a few machine laying around? borrow one.
Most likely the PSU, failing on the 12v...espec considering the age of the machine and most proberly has been runnimg a few usb items.
The thing with psu s espec older ones, they maybe rated at say 300W total BUT, even thu they will not pull that , one can still overload or run at the limit individual circuits.

With the current PSU pull the hard drive, video card (if has one and has on board) just have 1 stick of ram, and pull anyother cards/fans (not cpu fan) in the machine..then see.
9 times out of 10..will still fail, but at least u can be pretty sure its not one of those things.
look close at the condesors on the motherboard...looking for any leakage or swelling, espec in the cpu area.

Thanks for the ideas. I'll try pulling the cards while I wait for the used power supply to come. If nothing works I might throw in a $20 motherboard.

The power supply's thermal limit may have failed or is covered in dust or the power supply's fan has failed, but you describe a situation that is a common problem. You can blow out the dust in an older power supply with compressed air and at the same time make sure the power supply;s fan is free spinning. If not pick up a replacement.

More than likley just your power supply as this is the time of year most give out with the heat and as already mentioned any build up of dust in the cpu or power supply fans that aid in the process of over heating.

Computers should be servived like car regularly
Temp file etc, reg files checked, defrag and case blown out of to clear and dirt dust with filtered air...and dont let the fans spin up.

Steptoe, what do you mean by "dont let the fans spin up"

"dont let the fans spin up"
When u hit the fans with compressed air they spin....and electric motor is a generator in reverse...so when they spin up they produce current and voltage.
To stop them spinning up stick a nail or bit of wire, or end of a cable tie, what ever into the blades.

Unfortunately the different power supply didn't fix the problem. So now I need to decide if I want to take the whole thing apart and invest another $22 for a used motherboard or just find another different computer to put my hard drive in.

So u pulled all the cards no fix?
yep u have now established MBoard...did u inspect the condesors as I meanted about..I will lay odds u will find at least 1 that is swollen...that would have ided the issue way back
Get what we call an upgrade box here...cheap and if intel and gigabtte or asus mb reliable.

I tried pulling the cards and no change. I did not see any swollen caps, but I did see two caps by the printer port that looked a little crusty on top, brown dry crust. What is a good site for used computers and accessories other than eBay?

but I did see two caps by the printer port that looked a little crusty on top, brown dry crust
Yep definate sign pressure build up and leaked.

What is a good site for used computers and accessories other than eBay?
Cant help on that m8, I either build my own, or get my wholesaler to put together for mr if busy....well i will be honest here, I have put enough stuff thru them for 15 odd yrs they do it for free for me....hell it only takes 20 to 30 mins.
This machine Im on now I built in 1998, a p3 866 intel on assus mb...has been going full time since then, only turned off because of updates lol....most of my machines...no all arelike that.