Minsc said:With 12GBs of RAM you're definitely a candidate for a bad stick.It is possible Windows downloaded a high priority update and restarted on it's own, but unlikely, unless you just missed the alert that pops up when it does so.
If it continues to happen, do the memtest thing overnight. Nothing like breaking in a stubborn PC... so glad mine wasn't that much trouble!
One thing to note with memtest. I've had the best luck individually checking each stick briefly before I let it go though complete passes. Some sticks are so dead that it catches them right off. It's a little more work at the beginning--popping all those sticks in and out. But it saved me time in the long run.