have you checked the obvious things ? Is the volume on the handset turned up ? Or is it muted ?
If everythign seems OK, then try unregistering the handset, then resetting to factory defaults, then register again with the base station. If it still doesn't work, invest in another handset.
If you don't have the operators manual, type "Freelance XD500 manual" into google - it is freely available as a download - happy hunting
doctor phone, January 2009