IMHO, this is all one really needs to do in most cases. A full disk format and then a complete reinstall of Windows will sufficiently "wipe" any personal, sensitive data such that it wouldn't be recoverable by anyone who wasn't very determined and very technically skilled.
Message states that drive cannot be formatted if running windows from that drive. No other drives installed to format/reformat.
Am I missing something? I guess in this instance all that can be done is a clean install?