Explanation: During the installation of some OSes, the MBR is overwritten. Some of the System Commander code gets overwritten in the process, and System Commander needs to be reactivated.

To reactivate System Commander:

1. Insert the Boot Utility diskette #1, and reboot your machine.*
2. Select prompt only. 
3. From the A:\ prompt type CHECKMBR <enter>. 
4. Reboot the computer and OS selection menu should appear.

*versions 7 and above will run CHECKMBR automatically when the diskette is booted.