There might be instances where Windows is not able to format the USB pen drive or any other portable drive attached to it, in such cases you can try out Any Drive Formatter. Any Drive Formatter is freeware tool which will detect portable drives on your system and will allow you to format it. The application has simple interface and is easy to use as well.
All you need to do is to select the drive and enter a name for the drive. You can also select the quick format option available. This tool is really helpful when Windows fails to format some of the USB drives and other portable drives.
You need to run the application in administrator mode for formatting drives.