First off go to Machine Status > Tools > Admin Settings > System Settings > General > Audio and turn up the volume for the fax so you can hear its transmission and verify what is happening.
Fault Code 035-718: Target Fax is Not Answering Error 035-718 T1 Timeout, No Response from Sender Received. Job Canceled. Remote Device Will Try Again. (Caution Screen with [Close] Button) Message
Fault Code 034-791: No Answer Error 034-791 Check Line Connection. Please Disconnect and Reconnect Fax Line to Ensure Proper Connection. Job Canceled. (Caution Screen with [Close] Button)
If it happens to every number and not just one, the issue is either the fax line or the fax card. So unplug, replug, replace cable to eliminate the line before starting in on the hardware fax card.