Forum Moderators: phranque
IBM systems typically have a "service partition" that has a version of PCDOS installed on it. This may have recovery or diagnostic software, and I imagine that's hwere your "demo mode" lies.
I've removed the service partition from my system, as I don't find it useful.
Check your BIOS settings - there is probably something in the BIOS settings related to the service partition, forcing it to stay in the service partition, etc.
Boot into DOS from a floppy disk (I note the release in the past few days of FreeDos 1.0, and there are other free solutions), run FDISK, and see if the service partition is marked as the "active" partition. If so, mark the Windows partition as "active", and/or make the service partition hidden.