Find someone who knows how to use a digital voltmeter and then call Goldline's support #. They'll make you wait ~ 30 min on hold but then will walk you through what to test to find out which part is bad. Short of being able to do that, I'd start with the rectifiers
Then go to the diagnostic menu and click to the first entry. It should read the volts and amps of the cell. Report back.
If the cell were failing, current should drop but not voltage. Too much salt would tend to drop the voltage some but current will rise and then you should get a high salt warning and not a low voltage warning.
The PS-4 is notorious for failing in the power supply circuit, specifically a solder joint on the board which burns out. This can be diagnosed/fixed with this proceedure.
Did you press the "+" button while reading the voltage/amps to start the cycle over? Try that first. If it is still 0 readings then it sounds like a board failure which is explained in the link I posted above. Look at the proceedure and see if you are comfortable taking care of this yourself and make sure you turn off all the breakers to the panel before proceeding.
A lot of things can cuase the boards to fail. Bad design or manufacture is the case with the solder joints. Power surges are a major culprit in most electronic part failures. Even if you don't know there was a surge or spike it takes a toll on the components.