|Since you've tried to format the drive, I will presume that you no longer want the data that was stored on it. It sounds likely the drive is completely corrupt.|
The only way you can make the drive useable again would be to perform a "low-level format". This is where the FAT partition table is reset and literally all of the bits on the flash memory are set to 0s.
The best tool for this is called OnBelay. Download, install and use it to try and low-level format the drive. If it works, great, otherwise your USB flash drive might not have the necessary chip onboard it which allows low-level formatting.
If it doesn't work, I would recommend just going out and purchasing a new USB drive. They're incredibly cheap now.
Free PC Help forums