Incoming callers not able to hear a ring tone

We have a problem with inbound calls to our 800 number. What happens is that when a client calls our 800 number they do not hear the usual ringing sound, they only get dead air, the phone on the agent’s desk rings just fine, but the client hangs up thinking that the number doesn’t work. What it seems like is that asterisk is not playing the ringing tone back to the client.

In addition to this little hiccup, the system doesn’t seem to be passing the call from one agent to the next (like call hunting). What I mean by this is that we need that 800 number to ring agent 400, if 400 doesn’t answer then ring 401… up to 404.

Thanks in advance.