Well, first off, never ever EVAR install the nVidia drivers from the nVidia site onto Ubuntu. It does not properly install things and it messes up your system in indescribable ways and things are gonna be bad. Always use the Ubuntu packaged versions on Ubuntu. Canonical and nVidia have a cross-company team dedicated to making everything work properly between the two parties (and certain other, significant, third parties).
Second, your symptom was that Unity was not starting, which is unlikely to have anything to do with the nVidia driver, since the X server is obviously running (you're seeing a graphical interface). The log file for Unity is ~/.cache/upstart/gnome-session.log, and that's what you need to make sure gets included in the bug report you file. You should file a bug report by using ctrl-alt-T to bring up a terminal, type "ubuntu-bug unity<return>" and follow the direction on the screen. That program will gather information on your system configuration and include it in the bug report.
If you're still having trouble, come back here and let me know.