This could be several things. Most likely is that the telephone itself is either out of service (unplugged) or defective, or forwarded directly to voice mail. If you go off hook and hear "bouncing dial tone" then it has been forwarded. Un-forward it to fix the problem. If that's not the problem, then contact your telephone system support person. Hope this helps.
Answers & Comments
This could be several things. Most likely is that the telephone itself is either out of service (unplugged) or defective, or forwarded directly to voice mail. If you go off hook and hear "bouncing dial tone" then it has been forwarded. Un-forward it to fix the problem. If that's not the problem, then contact your telephone system support person. Hope this helps.