Check the running processes with either "ps -efl" or "ps auxww", look
 for references to shutdown/init and try to figure out what's going on.

 I'd guess there's an uninterruptible process running, init's trying to
 stop it but can't. You need to find it and try killing it, possibly a
 "kill -9" though be careful you know what it is you're killing.

 You could also try "init 6" or "reboot -f" to see if either of those
 will successfully restart your system.