PC freezes when idle, doenst while gaming

Hi,

Im having a little problem while trying to revive my old parts to make a media system.

The PC will freeze while idle (all power saving options are off, no screensaver) within a minute or 2 of having logged on. However if I decide to run a game or even play a video the system will not freeze, i can happily alt-tab out or leave it running in the background and complete normal tasks on the system.

Ive also tried changing components (ram, gfx-card, soundcard/onboard, psu) to no avail. Only components i havent been able to test are the mobo and cpu, being socket 478 its rather tough haha…

well any help would be appreciated, im currently stumped.

thanks in advance!