undable to su to root

Hello,

I am running RHEL 7.1 - 64bit. I am trying to su to root. Every time I try, I get the password prompt, then type my password. I get the following: Last Login: ......... on pts/1, then nothing happens. So it actually logs me in it seems, but I get nothing after that. It was working fine last week. Anyone have any idea what could cause the problem?

Thanks in advance.

William