Look very closely at all your assignments that relate to visuals and movement. Something is in conflict. There are two devices trying to ocntrol the hat switch. Check any addons recently installed. Do you use anything like TrackIR, EZDoc, etc.
Check %appdata%/Lockheed Martin/Prepar3d v4/controls - - rename STANDARD.XML and let P3D rebuild it - that's where all your assignments are stored. If it now works - compare the two files.
Good luck,
Vic