Well, here's my problem: Yesterday my system crashed for some unknown reason.
After rebooting, the bootup sequence stops while booting into the Desktop Environment.
Detailed Description: The system boots up normally, the Nvidia-Splashscreen appears, the screen turns blue, as usual, booting proceeds for some moments, but stops after a while. The only thing to be seen is the cursor (clock), which can be moved around the screen.
So, the X-Server doesn't seem to be the problem. Any hints? I really won't like to set up my system again...