From experience I know what might have caused your problem, Impudicus Rex. In my case, and about 90% of the cases that a computer reboots spontaniously, it's the power supply. It just can't handle all the power needed. Companies just put in a power supply that is too light for the job, because of the simple fact that a lighter power supply is cheaper. With all the things attached to a computer, like webcam, graphic tablet etc. the power supply is just too short on supplying the power needed. And especially when you render a computer eats up a lot of watts. Also a lot of people don't know this, but if you upgrade your internal memory or put in a faster processor it means it's heavier on the power supply. In fact, there's still no virus known and no program that will just reboot your computer just like that. It will always give you a blue screen or whatever first before shutting it down or rebooting it. There's one virus that will shut your computer down, but that means it will never start up again... at least not with the programs you had on your HD. I had the same problem and bought myself a heavier power supply (400 watts now), installed it and ever since no spontanious reboot of the computer. Went through a lot of trouble before discovering what it was. Later I went to forums with specialists on that subject and they did tell me the same thing, although it was already taken care of. Just check how many watts your power supply is now and go out and buy yourself a heavier one or see if you can borrow one and try first before buying. I'm sure it will help. Hope this will help you. Finest regards, Johnnie...