I have a pro Savage DDR card (pretty old), and it is freezing a lot here too.
What I do is this:
ctrl+alt+f2 puts me in a console. Just a console. From there, I log in using my username/password.
Then, I type startx -- :1
Whenever it freezes, instead of powering off, I type ctrl+alt+f2 until I am back in the console. From there, I type ctrl+alt+f7 (or f8), and voila, I am back in gnome, and it is okay again.
It is a nightmare, but it'll have to do for now (upgrading has gotten me nowhere), but whenever the computer freezes, the console is probably informing em of a GTK error.