Sounds obvious but did you happen to turn off the water valve behind the toilet the last time you used it? (Assume your AS has a valve there, ours does!)
Otherwise, maybe there is problem with the foot valve for your toilet - maybe you could try disconnecting the feed pipe to the toilet to ensure water is getting up to the toilet itself and help isolate the problem.
Brian & Connie Mitchell
2005 Classic 30'
Hensley Arrow / Centramatics
2008 GMC Sierra SLT 2500HD,4x4,Crew Cab, Diesel, Leer cap.