My USB Device is Showing Write Protected

I can’t format my SanDisk 8GB USB drive. I can’t even copy paste any of the files or folders fro or into the USB drive.
The disk is write-protected
Remove the write-protection or use another disk
Removable Disk
I am seeing only the message that the disk is write-protected. I have tried it on different USB port, but the result is same. I have also tried on different pc too. Is his the result of virus attack? Or any kind of physical damage has occurred? I have got some important files on that drive. Please give me a solution to fix up the USB drive and get all my documents.
