Perhaps, you can try to assign a new letter tot his drive in "Disk Management" and format it for rebooting it manually.
Is there something important?
If there is, you'd better try a free USB drive recovery tool
for saving your data back before you format this drive. You could visit this freeware here: http://www.freeware-fix.blogspot.com/2013/02/usb-drive-not-recognized.html
In the future, you must learn to back up your data well all the time.