Ordinal 175

Win2k server SP4
After the login screen I get this message and nothing else happens. If I go to the task manager I can start app by the exe’s but htere are no icons on the desktop, Also client machines can log into the server. Even with termserverfrom one of the clients still get a blank screen??
Error message (the ordinal 175 could not be located in the dynamic library userenv.dll) I have tried to replace it with a different one, no difference.
Thank you
John