installed ubuntu LXDE, can no longer log in

[Jeremy]

I just installed LXDE, simply using the sudo apt-get install lxde command, and now I can no longer log into my computer. I did not do anything other than run the install command, then I typed sudo startx to start running LXDE (apparently I didn't have permission to run 'startx' as a normal user, so I just did sudo).

When LXDE started, I was not logged into my account by default; it was instead logged in as root. I tried to type "login", and I then proceeded to type my username and password (username 'Jeremy'. I'm not sure whether or not I needed the '@Villa-Netbook' or not; but regardless, I doubt that this did anything detrimental), and it said "invalid login". I did not think at the time to try typing '@Villa-Netbook', unfortunately.

So I restarted my computer. Now, when I type my password into the ubuntu login prompt (no matter which desktop environment I choose), the screen simply goes dark and restarts the login screen. The computer doesn't shut down, tell me my password is incorrect or show any error messages or anything--it just brings up the login screen again and plays the ubuntu login sound. In fact, when I type another password, it actually says "invalid password". So I know that my password is still correct, it just won't log in properly.

I'm not sure what happened, or where to even start about trying to find the problem. I assume I'll need to login as a root user and change a file somewhere, but again, I'm not sure what to look at first, since I didn't edit anything in the first place. Any help or suggestions would be greatly appreciated so I don't need to do a fresh install.

UPDATE: When I'm logged in as a guest, I cannot do su or sudo. When I do su, su - or su root and type my password, I get "su: Authentication Failure". And when I try to do sudo, I get "sudo: unable to change to sudoers gid: Operation not permitted".

information:

Ubuntu 12.10

guest-QlD7L8@Villa-Netbook:~$ apt-cache policy lxde
lxde:
  Installed: 0.5.0-4ubuntu3
  Candidate: 0.5.0-4ubuntu3
  Version table:
 *** 0.5.0-4ubuntu3 0
        500 http://us.archive.ubuntu.com/ubuntu/ quantal/universe i386 Packages
        100 /var/lib/dpkg/status