No Maps Found
First, plug in your device to the computer where it is normally used.
Open TomTom Home and see if there are any Backups to restore. If so choose to restore the backup. This will return the device to a previous state that will require it to be updated again.
During update, if you are asked to remove software from the device... don't remove your map. This is what I did because I thought the device would be smart enough to know that it needed a map to operate, because it warned me not to remove all of my voice files because it may cause my device to fail... not the case. Make sure you leave your map on the device.
If there is no backup to restore (which is what happened to me) you will need to go to "Manage my [Device Name]" in the Home Software. Click on the "Items on Computer" tab. See if the Map file is saved on your computer. If it is there, click on the "more info" link under the map and you will see where this file is saved on the computer. Take a note on this path so you can navigate there with "My Computer."
Once there, right click the ".zip" file and select "extract." Choose a location to extract the files (I used my desktop).
Once the extraction is complete open "My Computer" and locate the TomTom Device. Right click the device and select "Explore." Make sure you can see this folder and the extracted folder on your desktop. Drag and drop the extracted map folder to the device folder (It should be placed in the root directory of the device, not inside an existing folder on the device. This move will take about 30 mins depending on the size of your map. Once complete you should be able to disconnect your device and restart it as usual.
Make a backup of your device using TomTom Home software.
If all else fails, call TomTom Support or keep searching the net.