Needed to remove junk from a USB thumb drive. Google search yielded a nice find at http://www.bleepingcomputer.com/forums/t/219693/unable-to-format-usb-stick-to-full-capacity/
1) Type “DISKPART” from the Command Prompt (accessible by clicking on Start and then typing “cmd” into the open field); you will then see the following prompt: DISKPART>
2) Type “LIST DISK” to see what number your USB drive is listed as.
3) Type “SELECT DISK 2” (if your USB is disk 2; replace # with your disk #); Diskpart will confirm that “Disk 2 is now the select disk.”