In the past week I am no longer receiving faxes. I colleague informed me she was unable to fax, and then I tried faxing from my Sonic Fusion phone line to the fax, and it did not connect.
I've just used the Member Tools -> Labs -> Send a fax function here to send a fax to my FaxLine. Sounds a bit circular, but it should be a valid test of both sending a receiving capabilities. Refreshing fax history showed it progressing to process, transmit, and then I received the confirmation of transmission and then the received two-page PDF and cover sheet.
Will you try sending yourself a fax via the Send a fax link in the Labs section of the Member Tools?