Win 2k pro not letting you log off

I am the help desk technician for Naval hospital. We are currently using dell pc’s with win 2k pro as os. Recently I have encountered users calling saying they are not able to log off. No error message. When they hit ctrl alt dlt or when they hit start logoff pc does not respond. Mouse is still responding.Only solution I have found is by shutting down pc. Anyone have any situation like this and if so what was the solution.