My sister and I are trying to fix mom's computer ...
Here's the repair history:
1. computer doesn't power on so something got fried, not sure what
2. so sister bought a new PSU and installed it; result: computer still didn't power on
- sis took mom's old PSU and installed it into her computer, old PSU works okay!
3. bought a new mobo and I installed it; computer starts up and I am able to get to BIOS then machines shutdown by itself after ~15 seconds everytime
4. to eliminate possibility of shorts, I disconnected everything from mobo except 24pin main power and atx12v 4pin cables, 1 stick of RAM, monitor and keyboard. Placed mobo on cardboard and I shorted the power switch to power up the computer; result: same, shutdown after ~15 seconds
Needs more Thermal grease?...not good,do it right or not at all.
IMO..bad cpu?...short in case/switch wiring?....case to M/B short?....RAM?
Have you tried setting up outsde of case?
What exactly happend?
That Pentium D will shut down in 15 secs, if the cooling is not sufficient. If nothing has ever been done to the board, get a new CPU heatsink and fan, install it and try again. I use Arctic Cooling Freezer 7 Pro on my 775s. Since it doesn't sound like your mom is overclocking, you could find a cheaper one. Make sure the "thermal grease" is present on the new heatsink - if not, you'll need some to provide adequate heat transfer from the cpu to the heatsink.
If you replace the HSF, and still no start, you may have to get another CPU.
I installed a new heatsink + fan combo on the CPU and SUCCESS!
The computer works as expected. My mom is very pleased ...
Only thing that sucks is now my sister has to reinstall Windows & apps all over again, since the original motherboard was discontinued and had to install a different one.