sounds like one of the buttons has gone. Get this every now and then on laptops and even on a kindle fire (one part of the screen was convinced it was being repeatedly touched).

Try disconnecting the keypad, if it's a dodgy key then that should at least let you use the printer via usb while you get a replacement keypad.

If that doesn't work - check all the power connections to the motherboard. one could have worked looses. But sounds more like stuck keypad key to me.