Computer Problems, Dont know if its the Psu, Mobo, cpu or graphics card

I got a computer from a friend of my fathers, he wanted me to fix it. He said it had been turning off automatically every ~20 mins and wouldnt turn back on for a while. When i got it i opened it and cleaned the dust out, there was so much dust on the heat sink that i doubt the cpu was getting any air. Anyway i cleaned everything then hooked it up and turned it on, it wouldnt boot up and the monitor screen stays blank. I had a few suggestions from a few people. One person says it could be that the power supply could be sending too much voltage and the mobo was turning itself off. Another said that it could be the cpu burned out. Another said it could be the graphics card burned out, or the power supply burned out. Im not sure what to do now and if anyone has had a problem like this they could help me out. thanks.

Specs: AMD Athlon 64 3700+, nVidia GEForce FX 5200, MSI AGP 8x mobo

 

What power supply is used in that computer? Also if a circuit has been burnt, it would have a very ugly smell.

 

OK. ((edit)firstly, watch out for static electrical distcharge, it can ruin a pc in a FLASH, if you can feel the static bolt, it is over 2000volts)
It was working (almost) before you cleaned it out, so just carefully check everything is socketted properly and is plugged into where ever it is suposed to be.

It sounds like it was a dust caused overheating problem, so you're on the right track.

If you have futher problems, try disconnecting the harddrive power cable, and try to boot.

If you get a post screen then you may have found the culprit.

You may need to do this for the ram, graphics card, and any other cards that are installed. (but do them one at a time, to find the error)

The cpu... Make sure that it is seated in the socket fully, and that the heatsink and fan are attached and the fan is plugged in. (if the heatsink is not seated correctly the system will shutdown automatically as before.)

Don't go changing the bios configuration, as the system worked before it should work again witht he same settings.

You have a pretty common problem, so be patient and do things methodically, you should find a way through to a working system and cudos for doing a good job.

Static is your enemy......
Regards Glenn