After doing lots of google and various trials , I was finally able to get the reason for the above problem.
Note: The same error can occur for various reasons, so my work around might or might not work for you.
The problem was with the permissions for the /tmp folder.
The permissions for the /tmp folder should be
some one had changed this to
So other than root no other user was able to start the Xserver session.
once I changed the permissions using :
sudo chmod a+rwxt /tmp
every thing is working fine.