Here's what it says:
Your session only lasted less than 10 seconds. If you have not logged out yourself, this could mean that there is some installation problem or that you may be out of disk space. Try logging in one of the failsafe sessions to see if you can fix the problem.
View details (~/.xsession-errors file)
mdm: DEBUG: Forking extra process: :etc/mdm/PreSession/Default
initctl: Unable to connect to Upstart: Failed to connect to socket /com/Ubuntu/upstart: Connection refused
mdm: GLib-CRITICAL: g_key_file_free: assertion 'key_file !=NULL' failed
mdm: DEBUG: Running for marie on :O
and I'm using Cinnamon if that matters. Solutions and other tips/info will be appreciated, thanks