Thought about that, Cloudy....but if it's intermittent, even removing a module or two (or three - I have 4 x 2Gb) it still might not show.
I like the dry joint idea - though how does one test it?
Temps? I tend to leave the machine running from eyes open (7:30?) till eyes closed (midnight, 1am?). Turn off the two LCD monitors when walking away from it. It auto checks for e-mails every five minutes and gives itself an MRI, as it runs its various scans every day.
So it cooled overnight for six to eight hours - *then * it wouldn't start.