The monitor powers up and displays information, but one or more of the buttons on the monitor face (usually the Menu or Menu | Back button) do not work.
This is a hardware issue, usually caused by corrosion on the circuit board. The PM must be replaced.
Not all buttons on the monitor face power up the monitor. Only pressing certain buttons or rowing/skiing will power up the monitor. After the monitor is on, some buttons may not work unless pressing hard.
The keypad may be aging or worn and cannot make the connection. The PM3/PM4 keypad, part number 1451, should be replaced. See also: