This morning I had some updates for my Ubuntu 13.10 system so installed them but when I rebooted my PC and logged in via the graphical login screen it just returned me to the login screen rather than loading my lightdm desktop. Effectively a "login loop" This was pretty annoying as I could not figure out what could cause it and tried various things with out success, such as deleting my .Xauthority file and rebooting etc In the end I tried reinstalling the nvidia driver as described in my previous post: http://www.boliston.com/2014/01/03/installing-nvidia-driver-in-ubuntu-13-10/ and amazingly I could then login normally again. I noted also that the "latest" nvidia 64 bit linux driver is now 319.82 (released 10th Jan 2014) rather than 331.20 (released 6th Nov 2013) so the driver filename is now NVIDIA-Linux-x86_64-319.82.run rather than NVIDIA-Linux-x86_64-331.20.run I therefore installed the latest driver as per my previous post, simply remembering to substitute the new filename for the driver.