I've encountered a similar problem as Nvidia driver updated - mixed versions of 304.88 and 319.32 and Ubuntu 12.04 LTS - Black Screen at boot After changing Nvidia Driver
Using what I found there, I was able to purge the nvidia version 304 and reconfigure version 319. Now my problem is that I can get to the login screen for unity, but I can't get past this screen. I enter my password and I just here the drum sound and the login screen comes up again.