The roller mechanism may be defective or broken in any number of ways.
But also, the rollers (*if* they are in the right place and cams and gears associated with them are not defectve) may need cleaning, esp. if the printer is several years old or has had high usage or both.
To try it, if you like, follow this procedure:
If the problem might possibly be owing to aging roller surfaces (for paper is fed into faxes and printers with rubber or plastic cylindrical rollers, that propel the sheet into or through the machine)... then you might need to clean the rollers in the problem area where feeding is not happening.
Remove all paper from the machine, unplug it, and open it so as to have access to the rollers in the problem area where feeding is not being done properly.
Take a clean high-quality lint-free rag cloth, moisten it with rubbing alcohol, and rub the rollers firmly all over their paper-contacting surfaces, three times over.
(If the rollers are hard to reach, there is another way to clean them... let me know if that is the case, and I will detail how to do the cleaning.)
Allow 5+ minutes for drying-off, then reload the paper, close up the machine where you opened it up, and then try again.