Forget about Map disks for the time being. Your navigation computer is locked and is not making its presence known to the rest of the system. That should be your only concern until it is solved. It will not have been solved until you have a navigation option in your main menu. No use loading disk after disk in the unit before that happens.

Now then: Check that there is power in the 12V wire in the Mk-III unit. See if any LED do blink or light in the unit in any situation. If not, check the fuse. If fuse OK use a volt meter or rig a 12V lamp to check power at the connector.

If power is OK you have to re-install your Operating System. Find and download V24 USA -EEUU in spanish- CD image file. Make sure it is an image for a Mode2/Form1 disc. Burn it and use it to re-load your firmware. There are lots of threads in this forum describing the procedure. Follow it strictly.

Good luck