Here's the history of that "GPS Fail - Press ON" message.

The Display and the Flight Recorder are two separate microcomputers
running two separate programs on two separate processors. They
communicate with each other using an asynchronous protocol. If, for
any reason, communications cannot be established, the Display gives up
and displays that message. In the early days, the protocol was
experimental, and some unrecoverable errors occurred. Pressing ON
restarts the Display microprocessor, and that took care of the
problem. Later, the protocol became more robust, and it is very
unlikely that a communication failure today is a failure of the
logic. It is FAR more likely that the fault is an open circuit
(broken wire or connector), and in this case, pressing ON does not
solve the problem. A better message would be: "Communication failure
between Display and FR. Check cable."