|What specific model is it ? |
Some models have a security feature.
You must either
- move a tiny switch on it in to a certain position in order to be able to Format it (or delete it's data or write data to it).
- or - it may have software installed on it that requires that you supply a password in order to be able to access it - it you can access it, then you can enable the ability to Format it.
If it isn't your flash drive, any flash drive may have had software installed on it that was installed by someone other than the manufacturer that requires that you supply a password in order to be able to access it.
You CANNOT delete the partition(s) on a flash drive or a memory card in Windows 2000 and up due to Microsoft's wishes, then make a new one then Format it (in Windows 2000 and up both things are done in one step) but you CAN just Format the drive, by RIGHT clicking on it's drive letter, e.g. in Vista or Windows 7, in Computer or Windows Explorer, and choosing Format, or you can just Format it in Disk Management.
Oops - I missed this...
"how to format raw pen-drive"
Flash drives always come already software partitioned (using the FAT32 method in most cases) and formatted when they're new.
If your flash drive shows up in Disk Management (e.g. type: diskmgmt.msc in the Start Search box to go there) as it's data space being RAW or un-allocated, the most likely thing is you, or someone else, have DAMAGED data on the drive because the flash drive was unplugged while Windows was running WITHOUT you or whoever having clicked on the Safely Remove Hardware icon in your taskbar lower right on your main desktop screen and choosing to STOP accessing the drive.
(That icon may be hidden - if you don't see it, click on the arrowhead at the left end of the icons there to show hidden icons to reveal it.)
You CANNOT successfully just Format the partition if the reason it's showing up that way is the partition table data for the partition is damaged.
If you're not concerned about data you know was on the drive previously that should still be there, you CAN fix that problem by deleting the partition(s) on the drive and making (a) new one(s), and then formatting the partition, however you CANNOT delete the partition(s) on it in Windows itself due to Microsoft's wishes. You have to use third party software to do that, that can actually delete the corrupted partition.
If you ARE concerned about data you know was on the drive previously that should still be there, or in any case.....
Usually the reason the drive's data space shows up as being RAW or un-allocated is the partition table data for the partition has been damaged.
If the partition table data is damaged, you CANNOT successfully just Format the partition.
If you use a program that can repair that partition table data damage, you will probably be able to see all of or most of the files and folders that you know were on the drive again.
Sometimes other data is also damaged, but in most cases if the partition table data damage is repaired, you will be able to recover all or most of the files or folders.
E.g. if the flash drive is using FAT32 software partitioning, there are two identical copies of the partition table for each partition, only one of which is used. If there is nothing wrong with the second copy of the partition table, some programs can make the partition use that second copy of it.
Troubleshooting USB device problems including for flash drives, external drives, external memory card readers.
See Response 1: