OpenGL applications seems to freeze my system

In my SuSE 9.1 system i installed nvidia drivers (i have tested both 6111 and )but from time time the system hard-reboots itself. For example if i start the system and try to play doom3 its ok. If i exit from doom3 and then start it again then is possible that my system reboots. The same problems apperars with matlab 7 (which uses opengl). First time ok, second time reboots). And when i mean reboot i mean reboot like presing the reset button.