Long time ago I had a similar kind of problem with some games, but not all.
Back then I used 3D mark to find out whether its results have changed at all - sure had, it locked up.
Eventually it came down to GFX drivers, which I couldn't fix by reinstalling the drives and had to dig up couple of months old registry backup which fixed it.
I think I had one of the first generation Radeons back then.
Some more guesses which aren't quite so likely...
Also few other things can cause such lockups:
CPU overheat
Direct-X problem
Chipset driver problem
Also likely things, but which I don't think would be it:
Low voltage from PSU
RAM chip is fubarred
Soundcard driver problem (hardly likely I'd say)
My best guess goes for the display drivers or other files/settings related to graphics.
It sounds very much like the problem I had a long ago.
I just don't know what caused it... I was lucky to have a backup of the whole windows registry.
Since then I've made registry backups roughly every month.