Speed hold for 737 doesn't work!!!

Hello.
I have had an issue for a while now and I have done a lot to try and fix it with not result. I can't engage the autopilot speed hold for the default Microsoft 737-800. I have tried reinstalling the aircraft, reinstalling the entire game and verifying the integrity of the game through steam. It used to work but just one day I came home and the aircraft wouldn't work. If anyone could help I would be extremely grateful. 🙂
Thanks a lot,
Jack Stevenson.[/b]