Husqvarna Proflex 21 just stopped engaging the blades. Was working fine, on starting the next cut the engine goes well, lever works but no mower blades turn when lever lowered. The spring to the blade brake appearred disconnected, with the arm hanging down; reconnected but still no engagement or engine pick up in revs. Seat cutout functions fine to kill engine in mowing position. No grass blocking levers. Is there a hidden microswitch somewhere or other checks?