I don't think your problem is X. You would not even get the Login screen if X was corrupted, right?
Compiz might be the problem. Boot in recovery mode reinstall/remove compiz, then reboot. *might* solve your problem. if not most probably your kernel module for NVIDIA is corrupted, reinstalling the driver or kernel might solve the problem (It happened to me once), also you might want to post Xorg's log file here. Mahmood -- Ubuntu Bangladesh mailing list ubuntu-bd@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bd
