It's worth trying the "ClearFlash" utility.
No promises, but it often fixes "No maps found" problems.
Get it from
http://uk.support.tomtom.com/app/answers/detail/a_id/6178
Don't expect anything exciting on either the TomTom or PC screen when you run it, you hardly know anything has happened.
I've no idea why, but some people have suggested you run it three times. I've only ever needed to run it once, but it won't do any harm to try it several times.
Also, check to see if the maps are available if you run the TomTom from the PC emulator in Home (called "Operate my Go"). There seems to be a common issue where the maps are visible there, but not standalone.
You can also try adding a new Favourite and planning a route while in the emulator, as that has been known to get the maps recognised properly.
Otherwise wait for other replies.