My 8gb pendrive is showing free space 0 bytes and toatl space 0 bytes and is also not formatting,what should i do?

You should format it through DOS...rate my answer

Have you figured out why this 8GB pen drive shows 0 bytes used and total space and asks you to format before any access? Is it displayed as RAW file system in Disk Management? If so, do not panic! From my understanding, the easiest way to convert drive RAW file system to NTFS is to merely format it on your PC or laptop as you usually do. However, if you do have performed formatting processes there several times already, you'd try it on another computer or other professional format tools online to take chances.
And one more thing, have you left any important data on this RAW file system hard disk? If you do, in order to rescue your desired hard disk, you've better take chances with external hard disk RAW file system recovery software.
NO matter what your situations are, learn a lesson to prepare drive data backups well from now on to avoid such hard disk data loss troubles.