Okay, try this software:
http://download2.lsoft.net/KillDiskSuiteFree-Setup.exe
For the installation, select Windows Version only (you dont need DOS or bootable versions).
Click OK after running it for the first time (no need to go PRO)
Then when you run the program tick your USB drive in the list on the left. DO NOT tick your hard drive or any other drive letters.
Then choose 'Kill' either from the menu or by right clicking and when prompted type ERASE-ALL-DATA. Choose First Pass: All-Zeros.
If you have any data on the drive you want to keep then back it up beforehand as it will be completely gone.
Once it has completed its RAW format (may take awhile) click Start > Run > CMD > OK
and type in
format x: /FS:fat32
Where x is the letter of the external drive.
Press enter again when prompted. Type in a name for the drive when prompted.
Hopefully that will fix it. I just tried it on my drive and successfully copied a file to the drive.