Computer turning itself off

[Hodsocks]

I am having some problems with a computer switching itself off, it may be after 5 minutes or 5 hours there is no consistency in it. When it does switch off the power light on the fron of the case is on but all the fans are off and when you hold the case switch in for a few seconds the light does go out.
I have ran checks on the hard drive, motherboard and memory and all passed without a problem. I have changed the power supply thinking that may be the problem but still no improvement. I don't think its heat related because of the wide variation in times that it stays on and the hardware monitor in the BIOS is reporting a processor temp of 50 deg C.
I have checked for Adware and virus's and found nothing. I am thinking that it may be motherboard related but the check in Microsocope reported no problems, is it possible to use Microsope to differentiate between motherboard and processor faults?
Any suggestions would be gratefully received

 

[Tedster]

is your thermal sensor shutting it off?
what are the temps on your CPU?

 

[TCool]

There might be a setting in your bios that shuts off your pc when it gets to a certain temp. I've also had motherboards that have had some sort of short against the case that caused it to power off. I'm not really sure of the exact cause of that, but you could try checking to make sure your motherboard is secure in there.

 

[Hodsocks]

The BIOS is reporting a cpu temperature of about 50 deg C, there is no shut off temp in the BIOS, it only monitors the temperatures.

 

[Hodsocks]

I think I have finally got to the bottom of this problem, I decided to fit another processor to see if that would cure the problem. When I removed the H/S/F I found out that it had been fitted backwards and also the processor was a Sempron 2200 not the Athlon 900 the BIOS was reporting. I let the machine run all day without a reboot with the new processor, I then refitted the original processor, once I had reset the jumpers to the correct fsb and it has been running Ok since.