Well, I'd test it with a thing called memtest. Let it run for a day or so.
Then I might look at event logs. They may offer a clue.
Might consider a restore point if this issue happened a few days or a few weeks ago.
Worse comes to worse, you may have to reload the OS.
I would get my important files off it right now. Save it to a web site like hotmail or other storage online. Or use a large usb drive or burn dvd's.
1/3 of highway deaths are caused by drunks. The rest are by people who can't drive any better than a drunk.