Arrrgh, well that puts a spanner in the works. Good luck with the reinstall, and take note of any Windows updates, driver updates etc when you do in case it happens again after any of them.
I'm assuming it just started suddenly, you didn't makes any software updates prior?
I'm also guessing you looked at obvious stuff like CPU temp etc.
Do you have Restart on BSOD enabled? If you can see the BSOD and make note of the error it might be handy.
In case you haven't already done this, go to Control Panel -> System -> Advanced, and under the Startup and Recovery section, click Settings. Then under System Failure un-check "Automatically restart".
Edit: but if it reboots before you can do it, I guess that's gonna be impossible