No Dial Tone/Calls going directly to VM

Was wondering if anyone could assist with an issue I am having. Our system has been alive for several month with no issues but now all of our users cant make outgoing calls and incoming calls go directly to VM. On the FreePBX info screen it shows that now IP phones are logged in and when checking the Linksys phone adapters it shows that the adapter cant connect to the log in server. Is this a service that runs in Linux that is not running? I am not sure where to start looking.