I just went in and saw my computer had restarted itself some time in the half-hour I was away from it. I don't understand why it would have done this. A couple of times it has turned itself off owing to a blue-screen error (the viruses which caused this have since been removed), but I'm pretty sure I had to turn it back on. Sometimes it restarts itself because of Windows updates to be installed - you get five minutes or whatever before it restarts automatically - but the thing is, I had unsaved Microsoft Word files open at the time, and I wouldn't think my computer would shut them down like that. I was only able to get them back through Document Recovery.
Anyway, does anyone have any ideas what else could make a computer restart itself for no apparent reason? My virus software has found nothing.