Before fax, you can connect an analogue phone or use the fax machine itself to test some normal incoming and outgoing and make sure that you are able to make calls using the ATA. if you are unable to make calls, it could be your Partition configuration issues.
if outgoing calls are working and only fax fails, you need to find out if it fails only for external fax or both internal and external. if it fails only for external most probably it could be due to the fax protocol.
do know what protocol your ISP support for fax, is it t.38 or passthrough.
what protocol you use for gateway ?
