In case there is still any interest in this......since you didn't identify the model of shredder I can only speak to the Fellowes PS30 . This shredder was designed by Fellowes NOT to be disassembled. you cannot take this one apart without destroying the plastic separators which keep the cut strip paper from wrapping around the cutter gears. This shredder does not have a "sensor" which senses when paper is put into the slot but requires that you push a button to get the paper to feed. Therefore, if the shredder will not accept paper, the problem is this switch. (which is NOT accessible).
The shredder WILL continue to work in reverse mode because of a separate path thru this same switch. R.Hand
R. Hand, October 2023
So the motor is good.
There's a micro switch that detects paper entry - it's the trigger for forward motion.
Reverse motion is not connected with the paper switch.
Check the switch - it may well be stuck or broken.
