interlock key insertion?

Without letting us know what the make and model of your shredder is, I can't see how we can give specific advice.
However, I suspect that your shredder has a removable panel, maybe to clear paper jams or to remove the bin, and this panel will have what's known as an "interlock" An interlock will be a device that prevents dangerous areas such as the rotating blades being able to run without the covering panels being in place in order to prevent you shredding your fingers. The interlock will be a metal hook attached to the panel that fits into a switch once the panel is correctly fitted. If that hook isn't located into the interlock switch, the machine will not run until it is..

Rupert
February 2020

No idea. You've not told us exactly what it is you are talking about

Gyu
February 2020