[QUOTE=Kerry56;2591129]Sounds like it might be a problem with the cpu heatsink/fan. Modern computers will shut down quickly if the fan on the cpu heatsink isn’t working, or if the cpu is heating up beyond the safe limit.
Check to make sure the heatsink is properly attached. And you might need to replace the thermal interface between the cpu and the heatsink.[/QUOTE]
Also is the FSB and CPU multiplier set correctly for your CPU?
It does sound that what kerry says is probably right.
To aid diagnoses it would be helpful if the monitor, keyboard etc is connected so you can see what is happening.