Computer has decided not to Recognize my TomTom????

Hi

I have had my TomTom talking to my computer fine and download a voice ect, then I unpluged and went a way, since I have been back to the computer the lead lights up the tomTom and the computer knows its pluged in BUT they are not talking, no TomTom home opens and a message comes up saying.
" hardware not recognized" or something like that

Please can anyone help me, whats wronge? what can I do I have tried another lead and it said the same .

Please help me I can not update with out them talking.

Thank you

Chel xxx