Oracle 10g2 on RHEL 5 - sqlplus problem

Hi.

I have jsut installed Oracle 10g2 on RHEL 5.  I create my listener
file.  Set my environment variables (sid, ld library path, etc) and
then, as the oracle user, I try to run sqlplus '/ as sysdba'.   It
does nothing.   Doesn't re****t an error,  just returns me back to my
prompt.

I have absolutely no idea where to start to troubleshoot this.   I've
been running this with RHEL3 for a couple of years now with no
problems.  I need to upgrade because the new hardware I am getting
doesn't sup****t RHEL3, but if I can't get sqlplus running, it is a
showstopper.

Please help!

Thanks!!

nuffi