Can`t format while using it!!!
It is not logical to format a hard drive that is currently in use.
Ways to do it:
- from another OS which is installed on another partition
- Hiren`s boot cd, System Rescue CD, or something similar
- Inserting the Windows 7 (or any OS) CD and rebooting.
In this case I think the best you can do is format the hard drive with the Windows 7 DVD and then install it again.
Another thing you can do is to try to repair the installed OS, but I would reinstall it.
Hope I helped