HP 1250 Fax series printer is disabled because,paper is blank when when it run through the printer.

I have an HP 1250 Fax series printer that is disabled because the paper is blank when when it is run through the printer. I suspect a sensor is malfunctioned. When I run the tests on the print cartridges – align, clean etc, only the align registers an error. What do you suggest. Would you accept a trade against a new similar machine.Printer showing the error it says error, retry ( meaning reset page in document holder and press ok).