Re: 7667 issues; black screen/ X windows crashing
I believe you're running into a Debian bug that results from an init script breaking the nvidia driver at bootup.
Did you ever install the Debian nvidia driver package on this system?
If you install the official NVIDIA 1.0-7676 driver package, does this problem go away until you reboot? If so, check in /etc/init.d/ for a script with nvidia in its name, and either delete or rename it.
If you continue to experience problems, please generate and post a full bug report.