Just do one thing go to My computer>right click>manage>disk management
select the pen drive there separately and format...... check it again
if it doesnt works then again go to same location select your pen drive and opt for delete logical drive
then again right click to form a new partition or logical drive..... select form a new logical drive and again format it completely..
Note: dont opt for quick format,,, let it format completely.
hope this solves your USB Flash Stick problem,....."
Source : http://ccm.net/forum/affich-22814-i-can-t-open-my-flash-drive