I actually had the problem a while ago with my usb. Make sure you have nothing usefull on your usb. Just in case.
Plug it into your computer, go to devices and printers. Right click on your usb, and go to properties.
Then click hardware and go to properties again.
Then click change settings.
Then click driver, and go to uninstall.
Eject the usb and then plug it back in.
When its finished re-installing right click it, and go to format, and change it to FAT32