How you cannot change boot device order?
Is this option “locked” somehow?
The whole story is somehow strange to me. Does this notebook belong to you? Have you bought it as used one?
The Toshiba disk boots in other notebooks without problems, until it detects that it is no Toshiba notebook.
How this can happen? Is this original disc you got with this notebook model?
Is maybe mainboard changed on this notebook?
Please tell us more about notebook itself.