1. boot as normal into Workbench.
2. Grab an empty/unused disk and put it into df0:
3. Format df0:
4. Open a shell/CLI and enter at promt "install df0:".
5. Now make a reset (ctrl A A) with the disk still in df0: -> it should boot into an empty cli-box
6. If not, your drive is :insane:
Markus