For some reason when I restarted my PC dual-booted with Ubuntu 13.04 and Windows 8, whenever I go into Ubuntu and I get to the lock screen and I put in my password, it will load, the screen will turn black, and it will go directly back to the lock screen again. This happens every time I do this. I tried using the guest account and when I try to log in with that the same thing happens. It was working just fine before this reboot, and now I can't even use Ubuntu. Please help!