I believe my problem is related, I have the same symptoms. The only way I am able to get into X is if I have only one monitor plugged in (to the DVI port) and the VGA port left empty.
-- nvidia card: hangs on start gdm if a second monitor on DVI-I is present https://launchpad.net/bugs/43710 -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs