Printers do not always indicate clearly if they are turned on. Make sure the printer is plugged into the power socket and the power switch is on.
Frequently, printers run out of paper in a high-volume situation.
Make sure the entire paper pathway is clear of sheets or fragments of paper. Refer to your printer hardware documentation before attempting to put any unusual paper or other media through your printer.
Be sure the baud rate of the printer matches that of the serial port.
Often, reseating the serial cable where it connects to the printer restores correct operation.
The use of the pins in serial cables varies somewhat in different applications. Cables designed for specific hardware may or may not function correctly with different hardware. Check your system Owner's Guide and the documentation supplied with your printer and cable to determine if the cable is correct for your hardware.