XP Messenger Makes sound but no Pop-up

A client has an XP box on a LAN and the messenger service is used for “net send” and “Right-Fax. In either case when a message is recieved on this workstation the service plays a tone but does “NOT” display a pup-up. It used to and nothing has changed. It happens with all profiles. The service is running. Anybody know why the pop-ups stopped? Oh Yeah, just to be clear the pop-up is not covered or hidden but is not there. Thanks in advance for any suggestions.