My PX1201 shredder will not stop running after a shred is completed X

Yes this is switch

If the motor will not run, then probably there's paper clogged in the shredder. Turn over the shredder, after unplugging the power cord, and remove the papers.

If the motor will run but not shredding any paper, then the drive gear has broken teeth. This is not usually worth fixing.
Hope this helps.

Most shredders will have a shred and a reverse setting. Is it running in reverse? Has the bin been emptied? With the power off, you can remove the bin and manually pull excess shredded paper jammed in the cutting heads -watch out, sharp metal . Once cleared run single sheets for the first minute to help clear rollers.

There is a safety switch somewhere under the top end assembly that closes when the shredder is properly positioned on the basket. Check to ensure it is making contact.

As for your first part - It sounds like there is something wrong with the switch lever that moves to complete the electrical circuit to start the shredder. On every shredder I have seen, there is a little "bellows" linked up to this lever that pushes it back so the machine will shut off. Most of the time all you have to do is put another piece of paper in and let that get shredded and the shredder will stop afterwards. If not, then just use the main switch to turn the shredder off.
Second, the beeping during "mid-shred" sounds like a warning that the shredder is starting to overheat and shut down. If this is the case, just wait a few minutes to allow it to cool down and try to finish the shredding you have. I have found that if you feed a shredder a constant stream of paper to shred, this might cause the shredder to overheat.
Also, the shredder may get overloaded with pieces of the shredded paper. Here is the way to check on that:
1. UNPLUG THE ELECTRICAL CORD FROM WHEREVER YOU HAVE IT PLUGGED IN.
2. Lift the shredder from the bin and turn it upside down.
3. Look for an excessive amount of paper in the bottom of the shredder. If there is a lot, you can remove it in several ways. (Most likely the bin is quite full at this point.) Pull the majority of it out and put it in the bin. If there are pieces of paper that you can pull out with your fingers, use a tool (needle-nose pliers, serrated tweezers, a hemostat, etc.) to get those difficult pieces out.

Replace the unit on the bin making sure that it is the same way you took it off. In most cases (on the better shredders), there is a notch on the underside of the shredder that needs to be on top of a "nub" that is on the edge of the inside top of the bin. Unless that nub is aligned with the slot, the shredder will not work.

Did you ever put shredder oil onto the cutting blades?????
The blades can clog with paper dust and then it can't shred as many papges as it should or even jam completely...you should occasionally shred a sheet of paper with shredder oil poured onto the sheet.

Common solution is to clean upper and lower sensors with cotton swab. If it still jams, then you will have to remove the top carefully and clean all paper shreds out of the housing. The paper shreds are most likely packed in the housing shroud and jamming or overloading the motor.

I’m happy to help further over the phone at https://www.6ya.com/expert/jayw_0e86fb055a7b73de

I have taken many shredders apart and found them so clogged up with shreds of paper and too much oil will turn into paper mud.Be bold and take the top off and clean it out. Unplug the power source and when removing the top , be careful because their will be a short cable connecting the top to the circuit board. Easy to damage.

I’m happy to help further over the phone at https://www.6ya.com/expert/jayw_0e86fb055a7b73de

Shredder drive gear is probably shredded - hard part to find or replace usually. Could mean a new shredder;-(