I have a Garmin GPSMap 556s which has let me down a few times. First it started freezing up and the power button never worked, had to unplug power cable and re-plug to get it working again.
Now the card reader no longer works, cannot read any SD card and the screen displays "Can't unlock maps " On startup it shows that it has built in Map Aus/NZ Marine Detail g2 Update v2013.0 14.50, but will not load it.
All functions work except I am locked out of the map and the card reader is not working. Have checked my SD cards on computer and they are good.
Have tried with the restore factory settings several times but it made no difference.

I have opened it up and there are no signs of corrosion. Is this too much information,

Am I possible wasting my time and should replace the unit.

Open to any advice, good or bad!