It's beeping because it's in programming mode. Usual reason with a machine of this age is that the touchpad has failed. Water gets into the touchpad membrane after a while, which makes the controller think a button has been pressed. If it thinks the STOP button is being pressed/held for more than 5 seconds, it goes into programming....
To confirm: Remove drip tray, take lid off controller box and unplug one of the flat plugs from the keypad (there will be two long thin plugs next to each other, and probably a space or two for extra plugs). When you get the correct one, the beeping will stop and the machine will resume normal operation on the working keypad.