Bizarre Reboot Crash

OMD2 worked fine for the first 20 or so hours I played it and even now I can start the game, mess around in the menus, start up a level and play and  even continue to the next level, but... if I attempt to return the campaign menu, the screen invariably goes blank, the sound freezes and then goes to static and either the computer reboots itself or I have to do a hard reset.
I've suffered this kind of crash on this computer with Steam games before (Fallout 3, Fallout: New Vegas and Skyrim to be exact), but that issue seemed to result from a faulty interaction in between my video card and the game engine in outdoor spaces and was solved by lowering my GPU clock settings.
I have tried both uninstalling and reinstalling the game and lowering the clock settings to no avail.
GPU:  HIS AMD Radeon HD 6800
 
Any thoughts?