What are you typing in to format the drive?
Are you using the drive when you try to format it, ie. Are you logged on to Windows and trying to format C:\?
The easiest way to format a drive is by booting to a command prompt or DOS prompt, once at the C:\> prompt type this:
C:\>format [insert drive letter]: and press the enter key. So it will look like this: C:\>format a:
Let us know if this helps.