What to do when it just won't work

[TheMacintoshLady]

I have been faxing away just fine, even when online with cable, with the 
native FaxSTF on X.2.4.
Sometimes the fax just stops working, so I reset all the prefs and reboot 
and then it works once again. Usually I wake up each day and find from 
5-20 faxes in there just fine, as it should be..........

Question: Tonight I'm tearing my hair out. I could use the OS 9 machine 
to take in the faxes but I will not be able to turn a particular fax into 
a PDF file using the reliable GlobalFax/Internal which is crucial for 
this person so I would like my X fax to work.

I have done everything, trashed, reset, run permissions/monthly/weekly 
and rebooted 4 times and now where do I look?
What modem setting should I be using for faxing? I am not on dialup so 
don't need v.34 or do I? There is v.90 and v.92 
I don't know much about modem strings, so which setting is best for 
faxing, since that is all I use the modem for?
Anything else I could have trashed and didn't?
Thanks.