My TomTom onev2 has lost its maps

My son used it to travel to dorset it was fine on the way up but the next time he switched it on it displayed a red cross over the memory card and it appears to have lost its maps.
We have tried to reinstall them from a compuer back up but it just says " No Maps". Does this mean I have to purchase another memory card with maps or what ? can any one help please.

Thanks
Richard55

[mikealder]

I would try formatting the device then run the "Clear Flash" tool at least three times before re-installing the backup, the clear flash tool can often resolve issues such as this with map activation problems, you can download it for free from Here - Mike