Check for error codes, but based on the issues it sounds like the board. The board should get 120VAC to it. Find the board which should be accessible without uninstalling the unit. Find a wiring diagram, it should be under the unit or online. Check for something that should be getting voltage by removing the harness at the board and see if the board is outputting the correct voltage. If it’s not it’s bad. But honestly a Maytag dishwasher might not be worth the trouble and money vs a new cheap one. If you don’t want to do either you can turn the breaker off, uninstall the unit and unhook it from the wires to stop the beeping. Or break the buzzer off the board if that’s where it’s located.