This question already has an answer here:
- Ubuntu gets stuck in a Login Loop 14 answers
Just install 12.04-64bit and while I can login using the guest login, I cannot with my user login: it just cycles back to the login screen. I have performed the sequence of apt-get update/upgrade and install of the nvidia-current driver, but got back that it was already in use. The password appears to be recognized, as wrong one results in an error. Have also tried switching to the 2D Unity, without other results.