Reviews, reviews, reviews...

Question: HP640 fax not printing

My HP 640 fax quit printing just out of the blue. It goes through the motions of printing, but the paper comes out blank. I've test printed and cleaned the cartridge, had the print cartridge checked at Office Max, and they said it was one-third full. I also cleaned the print area of the cartridge with alcohol. I don't know what else to do. Any suggestions?
Ray Kraemer