Did you have any software included when you bought the tomtom?
Ok dont delete anything try the following steps or double check what you have done?
I do not think a format was the option.
You can download the software via link
TomTom, portable GPS car navigation systems
Do not delete any of the folders!
Do not delete the files antitheftw.bmp, lowbatteryw.bmp and splashw.bmp
(if present)!