Do you have triple screen multiview mode ON? If so, you are not supposed to be able to change FOV. With multiview you can adjust the angles of the side screens by bringing up the multiview tool once on track by pressing Ctrl+= or whatever key you have mapped to it.
Adding to what @stonec says, for the triple screen Gizmo, if you don't have it assigned it's in Controls - MISC and it's call Triples/Tires
