Only thing I could suggest, if all other options are correct - is to try to remove drivers from safe-mode, with some utility like Drive Sweeper, or similar (google: nvidia driver remove), and try to reinstall it.
I should have mentioned that in my first post.. already tried that..
The only thing i can think of, is that it has something to do with Windows 8..
And i know.. i would go to 7 if i could.. but that's not an option..
But thx anyway!