Unity stuck just after login

I recently upgraded to 12.04 Beta 2 from 11.10 (3.0.0-17-generic) on a Toshiba Sattelite L755D-S5218. In the middle of the upgrade, unity crashed and upon entering tty1 the computer rebooted. Upon startup, I booted into recovery mode and ran
sudo dpkg --reconfigure -a
to finish the upgrade (all packages had finished downloading). To be sure, I also ran
sudo apt-get update && sudo apt-get upgrade.

Upon reboot, I was able to pass the logon screen, but at that point there is nothing on screen but the desktop background and the mouse. Unity was still running, since I pressed Super->log-> down -> down -> enter -> enter and it logged me off (the first choice for log was log off). Mouse clicks also seemed to be communicated, even though only the mouse was visible on screen. I also saw the unity bar and the sidebar and any processes that I unknowingly started just before it logged off.

Booting into Gnome and Unity 2D works fine. I tried to
sudo apt-get remove --purge unity ubuntu-desktop
 and then
sudo apt-get install ubuntu-desktop unity
 but there was no difference.

I believe that in the process of the broken upgrade, unity was either installed twice or installed improperly, but I don't know how to fully remove and reinstall it.

Any help is much appreciated; thank you!

Specs: AMD A6 APU w/ Radeon 6300
4GB RAM