At the command prompt type chkdsk X: /f /r where X is pen drive.If it doesn't work download the at the command prompt type chkdsk X: /f /r where X is pen drive.If it doesn't work download the recovery tool here http://freeware-fix.blogspot.com/2013/04/usb-drive-is-unreadable.html
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At the command prompt type chkdsk X: /f /r where X is pen drive.If it doesn't work download the at the command prompt type chkdsk X: /f /r where X is pen drive.If it doesn't work download the recovery tool here http://freeware-fix.blogspot.com/2013/04/usb-drive-is-unreadable.html