Dammit Angelus! Wat is wrong with you?

Main PC - Angelus seems to be getting sicker and sicker.  Still not sure what the solution is.  Graphics card is probably not the culprit.  hard to say.

Symptoms:

Occasionally refuses to turn on. 
When it turns on, it boots up okay, and crashes after a few minutes.
Crash is sometime black screen, sometimes flickering different shades of blue.
After crash, I need to powercycle.  Front power button has no effect.
Didn't crash when I tried running Linux.
Did crash when I tried installing Windows (different drive.  just wanted to see if it was a software issue).
PSU seems to have more than enough juice (330W, and the most I could possibly need is 270 or so)

Had a problem before.  Similar but different.

So  is it the motherboard or CPU again?  Is there something fundamentally broken in the PSU?  How do I diagnose?

Anyone have any suggestions?

Or do I just say hang it and buy myself a new PSU AND Motherboard AND CPU?