The machine will fax manually but will not dial the number on mem
With the little information, excluding make or model or mode of fax machine, whether feed through or flat scanning ( I even have one that does BOTH, and scans on a flat bed with a multi sheet feeder) I can only guess that somehow your memory is compromised.
Try this, in case you haven't already done so.
Set up the machine to fax a document over a short time period, like 10 minutes or so, from the time the trial begins and listen for the tones or pulses, and if there are none as you suggest, try thoroughly downing the machine for an hour or more, and reconfigure upon restart, as to date, time, fax mode, and so forth [the latter brings to mind the fact that your mode may be set to "manual," which would also account for your problem] and see if such a memory flush clears the memory, so that it can handle new commands.
Remember, before you start to check the present mode of the machine to determine whether it is set to MANUAL.
Manual mode will cause most machines to ignore commands like telephone numbers or future fax commands.