In the guts of the printer is a small plastic gear that drives the paper feed roller. This gear can slide sideways on the metal shaft that drives it until it no longer engages with the rest of the gears in the paper feed. If you remove the output tray, then holding a flashlight, you can observe the paper feed roller and see if it actually turns.
If the gear has moved sideways, you can probably push it back with a screwdriver.
I went a little further and carefully drilled an access hole in the underside of the computer. I then applied superglue to the shaft before I pushed the gear back in place.