Had this problem, too.
How about your case-box? Do the fans work properly and do they have a free flow to take the cold oxigen from? I mean if your case isn't near the house-heating. Try also open the case and leave it open for few mins while working with PC.
The fan: Did you buy the new proccesor? Because I think it didn't go suddenly that way, with blank screen, I guess you've changed some PC things. So If you did, for example if you bought new processor, be sure to spit some cold pasta on the fan to the side which touches the processor.
Mother board: I had once (3 month ago) a problem, I bought a new proccesor and it was overheating like hell, not because of home-heating, no because of pasta, but because of motherboard. When you connect the proccesor to the motherboard, it has to land successly, like there are 3 holes of the cable and I set it 3 holes into 2 sticks, so it couldn't accept some information and computer was thinking that my CPU is overheating, but it really didn't, but anyway it was restarting, too. I solved this with buying new motherboard. But you can also try to set it to other sticks. Hope you get it :D .