Did you check the intergy of the image of the operating system?
If not, it's entirely possible that there was an issue with the operating system's image, causing the program you were using to write the image to prematurely 'complete' the write; this would cause Windows to detect a hardware 'malfunction' (as it's trying to read a file that the partition table on the drive says exists, but actually doesn't) and would corrupt the partition table causing Windows to recognise it as a RAW partition (aka, unformatted).
You need to double click the drive and format it in
This PC, or
My Computer (depending on which version of Windows you're running) when it tells you the drive needs to be formatted before you use it.
If that doesn't work, you can try formatting it in Disk Manager or Windows' commandline partition management tool, Diskpart.
- Open a command prompt by using the key combination winkey + R
diskpart to launch the Diskpart tool- click 'Yes' when the UAC prompt comes up
list disk, find and note the drive number of your USB stick
- Now type
select disk #, where '#' is the drive number of your USB stick that you noted in the previous step
clean- this will completely format the selected drive
- Go back to
This PC, or
Computer, and try formatting the drive again, it should now work.
If this doesn't work, the USB drive is broken and you will need to get a new one. I'd suggest using a tool such as Unetbootin to download and put the desired installation image onto the new USB stick.
Do NOT use the same operating system installation image that you used before (if you must use it, redownload it!)