Root Login Problem

I have Sun Netra X1 Server which is headless means no CDROM, no terminal etc. I am connected it through serial port.
Accidently, someone in our department changed the root's default shell to /sbin/tcsh while there is no tcsh in /sbin and he logs off. Now, I am trying to logon as root on system but it said that no shell available. Unfortunately, there is no other account which is root equivalent.
Anybody has idea how to resolve this problem. Thanks in advance

The only way I know is to boot from Solaris CDrom in mini root system.
Go to this link to have complete procedure.

Thanks a lot, it resolves my problem.