I've got it, the Blue Screen of Death, Win 7.
My 5 year-old custom built computer is spontaneously shutting down and re-booting at least twice a day. I have 8 GB of G.skill gaming quality RAM, a Samsung 840 EVO 250 GB SSD, and a 1 gb IDE Samsung drive D.
I'm preparing to do my diagnostics now. Are we agreed that it is likely a hardware problem, either the SSD drive C, or RAM?
Suggestions?