Check that you have completely rebooted and that you have free drive
space.

I had a Linux install the other day that would allow user to log in,
yet not bring up the desktop. It was a matter of the hard drive being
too full, as freeing space brought everything back to normal. 4 GB was
free but deleting 8 GB more brought it back to life.

Something to check, based upon limited information regarding your
problem to go by.