gx620 dies, power light still on

I have a gx620 that likes to die, most of the time in the middle of the night, other times mid use. It is almost reminiscent of many gx270 problems I have seen.

Anyways, computer dies, monitor goes into inactive (amber light but not the disconnected rgb pattern signal). Power light is on, so I am not suspect of a power drop on the outlet. Power Supply and system board are both new since this problem started. My next step is memory, but I was wondering if anyone has seen this recently.

dell diags had no hit on the hard drive, or memory. I have heard the strangest things about these models failing, even from keyboards... so I am not dismissing any ideas. I was planning on running memtest86 next, and the pc keeps getting reset before I can see the codes on the front.