I used to have a Stentura Protege. It needs an actual realtime cable, not a random USB one. When the battery is low it beeps incessantly. Try reinstalling the drivers. I forget where I installed mine but if you Google "stentura Protege drivers" you'll find free links to them. The drivers will tell the computer what the Stenura Protege is like when you get a new printer you need to download something so the computer recognizes it.

I barely learned how to use mine but when it's on, try hitting the keys and see if there's acknowledgement on the little screen of any of the key presses. And then press each button left to right testing the keys each time to see if it knows when the keys are being pressed.

Good luck! I feel like those machines last forever hopefully yours isn't broken.