[puppypusher]

Seems to me that this hard drive was an internal drive recognised by the system as Drive “C”.

When you disconnected it and changed it into an external drive you changed the way the BIOS would recognise it. The only way I can see you clearing up this problem is by going into the bios and telling it the external drive is your boot drive.

It also matters where on the drive cable the internal drive is located but I think checking the Bios would be a start.

Good luck.

[perfect stranger]

Seems to me that this hard drive was an internal drive recognised by the system as Drive “C”.

Yes, it was. Now it's connected as a slave drive and the other partition does not show.