if u format ur pen drive. then use this step
-
Check out the registry under:

1)click on start button
2)clik on run dialog box
3)type regedit
4) HKEY_LOCAL_MACHINE\SYSTEM\CurrentControl…
The value 'WriteProtect' should be absent or set to '0' and when you try to format it you have to format it as FAT16

Or this might help you
http://www.sevenforums.com/hardware-...cted-disk.html