The OnBase Unity client requires a VPN connection while the web interface does not. You must log into VPN before launching the desktop Unity Client. If you do not have an active VPN connection, the Unity Client will keep trying to connect and the login screen will simply hang with no progress bar or visible activity.
If this occurs, go into Task Manager (by pressing ctl+alt+del keys) and stop the Login process. The Unity client will then error out. You can then start a VPN connection and start up the Unity client successfully.