HELP!!!!! how do i reomove 'write protected' message from my 16gb flash drive?

Costco should be able to check your purchase on their system even without a receipt.

You can also return the drive to SanDisk for a replacement.  And with them it is possible to smash the drive with a hammer before returning it.  Do verify that with them before doing it.

http://kb.sandisk.com/app/answers/detail/a_id/5232/~/return-material-authorization-(rma)-process