They have updated to a newer version of Teamcenter and NX. When they launch Teamcenter they get the login screen as normal but when they enter their credentials and hit ok the screen disappears and nothing happens, no rich client appears.
Solution Had them delete %USERPROFILE%\Teamcenter directory
Had them delete %TEMP%\v10000.xx.xxxx directory
Now the rich client starts correctly.
Notes and References
Hardware/Software Configuration Platform: INTL64
OS Version: 764