Help with overheating.

[phikhue]

We got the ECS K7S5A Pro from Fry's and tried to upgrade my friend's computer which currently had the AMD 900 MHz.
The computer was running fine with that AMD 900 MHz. We only put in a new motherboard (ECS K7S5A Pro), Athlon XP 2000+ (Palamino version), and a heatsink.
Everything seems to run fine at first, I was able to install Windows XP Pro and all the software that he needs. Then I play a simple game (Tetris 4000) and the computer just restarted while I was playing the game. It was weird so I ran Norton Antivirus to scan the harddrive and it restarted again. Now that I just left it alone and it would restarted by itself. We suspected something was wrong with the motherboard because we have heard a lot about these ECS motherboards (although I built 3 computers before with this board and no problem at all). I went to Fry's and exchange for another board. Again everything ran fine, got Win XP Pro installed and all the software. But after that, the whole PC got really hot. We left it idle for a while and the same thing happened again (shutting down and restarting). We could even smell something was burning. Shut it down and the power supply was hot to the touch. We thought Dawn it, cheap power supply. It is a Powmax 400W power supply that we got from CompGeeks. We pull the Antec 450W from a good running computer and put it on this computer to see. Running for about an hour and the same thing happened. The Antec was running really cool on the other computer but it got really hot when running on this computer also. So it's not the power supply. We tried one more thing. Turn on the computer, go into BIOS and run the AMI BIOS hardware monitor and watch the CPU and System Temperature. The CPU temp only showed around 48C but after a while the whole computer heated up (while we were watching the BIOS screen and doing nothing).
I am stuck now. All we were replacing is the motherboard, CPU, heatsink, oh and just 1 brand name memory stick PC2100. I tend to think it's the motherboard again but I already replaced it once with a brand new board (no return stickers for anyone who knows Fry's). I don't want to replace it again until I know exactly what the problem is.
Can someone help me with this? Thanks.

Phi,

 

[lsman]

so the HSF were with for XP 2000+ before. do you apply/reapply themo paste on it?

if it smell, ususally not a good sign.

 

[phikhue]

I did put good thermal paste on it (Silver 3 ???). The CPU seems to get good cooling since it only shows around 48 degree Celcius. I think the power supply got too hot and shut down not the CPU. The power supply ran pretty cool on the other computer but get very hot on this computer.

 

[phikhue]

Update:
My friend put back the Powmax 400W PS since the Antec had the same problem. He then unplugged the power connectors to the hard drive, CD-burner, floppy drive and re-connected them 1 by 1 and ran the computer for 1 hour after each connection. He now had everything connected back and the computer has been running for around 4 hours and still have not experienced the problem. It's really weird because yesterday it only took less than 1/2 hour before he could smell the burning. It smelled really bad that he thought everything was burning. Now everything seems to run perfectly normal.