Connect your unit to the computer (not Home)with the card in the unit and use Explorer to look at the contents of the card.
Do you see a bunch of folders and some loose files not in any folder? And is one of the folders something like Western_Europe? In other words, your map folder.
If so, use Explorer to make a backup of the card's contents. If not sure how, see here:
https://www.tomtomforums.com/genera...4-how-backup-contents-your-unit-computer.html
Now then, use Explorer to delete all the loose files on the card, NO folders or their contents.
Next, with the card in the unit, connect to Home. It should offer an application. Accept it and install. Now, disconnect the unit PROPERLY from Home using the Device disconnect icon on the bottom right of the screen.
Shut down Home completely and start up your unit. It hould boot up and say 'no maps found'. If so, that's good.
Next, connect to the computer (don't start Home) and use Explorer to copy back the map folder from your backup to the unit.
Disconnect the unit properly from the computer using the Hardware Disconnect icon in your notification are (bottom right -- green arrow icon).
Restart the unit. Working ok now?