Try rebooting the computer without any USB devices attached. Then plug in the USB drive, right click on My Computer, select manage, and then click ?Disk Management.? If the drive is not present in the Disk Management window or if you are not able to access it, then the drive may have failed. In this window you should see all of your connected physical drives, their format, if they are healthy, and the drive letter.
Change the drive letter of the drive. Right-click on the drive in the list, and from the resulting menu select "Change Drive Letters and Paths"
Click on Change so you can change the drive letter. Click Change.
Select a new drive letter from the drop down list, preferably the one that is not normally used for this drive.
Click Yes on the confirmation screen and you are done.
Caution: The cause of unpredictable behavior in a USB drive is often found to be the incorrect removal of a previously connected USB device. When removing USB devices right click on the ?Safely Remove Hardware? icon in the menu bar tray. This is usually found in the bottom right hand corner of the monitor. Once you have clicked on the icon, a menu with a single selection should appear. Click again on that selection to see the ?Safely Remove Hardware? window. Select the correct USB device and click the ?Stop.? When you receive the message that it is safe to remove the device, unplug the USB device from the computer.
Click Start and in the Run box type in cmd and press Enter.
At the command prompt type in chkdsk U:/r 'the drive letter that you just added:' EG: U: and press enter.
If it finds any discrepancies it should fix them.
Some good advice for the not so faint hearted can be found here.
https://www.techrepublic.com.com/5208-6230-0.html?forumID=101&threadID=234993&messageID=2519330
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