One thing you want to try when your system is in this state, is to either stop the X server, preferably gracefully, or do some remote-login to start a vanilla/previously working X server, which is going to reset the display(s) into a working state.

When debugging those pesky X problems, it's always simpler than to reboot each time ;-)

Now for the rest... I'm ouching for you my friend.

You are in luck, you did not get a black screen before ctrl+alt+fn... nvidia drivers are often broken, at least, less broken than ATI crappy ones...

What kernel are you using?

A few quick questions: Which Debian are you running? Which kernel do you have and which nvidia-glx are you using? If you SSH into the box, kill X and restarted X with the open source nv drivers does the box still work?

Messing with X is a pain, messing with closed source code is a pain and messing with buggy stuff is a pain, in this case you have a triple does of pain. I've been there myself and it's no fun...

--
  "It's Not Magic, It's Work"
    Adam