right click on my computer-->click manage-->click disk management from root storage-->assign a drive letter to the usb drive by right clicking the drive and click "change drive letters and paths". done.
You can also try this. It worked for me and came up clean on my virus scans. Just unplug all your USB devices and run this. The next time you plug in a usb device, it will act like it's first time, thus showing popups for new hardware found, installing device, your device is ready to use.