If you browse to the TT in the root dir of it, there should be a folder called something like, in my case it is called 'GB_plus_major_roads_of_WE'
Thats the map folder.....if thats not there your in trouble.....if it is the best way to proceed is to let the TT rebuild itself.
You should have TTHome 2.5 installed on your pc.
Make sure you have a copy of the map folder on the pc.
Now you do the following at your own risk, but it works for my TT510, so should work for them all.
Format the SD card with FAT32
Next copy the map folder back to the TT
Startup TTHome2.5, it will look for updates for your TT
Download and install everything it offers, rebooting the TT after TThome has offered an update......you repeat the download/reboot process about 3 times iirc.
Now it should be finding the map ok......
Finally
http://www.tomtom.com/6178Download and run exe , it flashes the TT bios to latest version
HTH
