is it a reboot to the blue screen of death or just a clean reboot to windows?

I was thinking virus, but if you're getting the bsd, it could be video/sound card related i.e. drivers, you might want to try some older ones,
or lighten up on all settings, shadows off, everything normal, not high, and if that clears it, slowly add to it.

Are you running stock GOTY, or have you swapped out files or added mods etc?

Are there other demanding games you play that work? Could be your vid card is getting hot due to a lack of in case cooling.All fans clear of dust etc?