Pen Drive not opening and not responding to cmd also.

Hello,
i have pen drive of 8gb sandisk it is detected by the system but it does not show any data bar. i can't even format it.i also used the command prompt to format the pendrive then the cmd is also not advancing to the further step if i do the same to any other pendrive cmd is completing it's task but while coming to this cmd is also not working.
plz if anybody know the solution to this plz reply.
if any one have any doubts plz reply. ThankYou..