This is an issue my Brother is having and one I'm unable to fix until Sunday, but I've got him to try multiple things including checking temps ( They are fine ), a new power supply ( working fine 800w corsair ) and turning off Windows Update as a test. Yet it's still doing this, it just shuts down when it feels like it, without ANY BSOD's or freeze ups.
He did tell me this however
Thanks guys!

He did tell me this however
This actually all started just after a windows update. It forced my pc to shut down and then when it booted up it would shut down every 20 minutes or so
Thanks guys!