I find that if I leave the three point lift arms in full droop mode (lowered all the way) but something prevents them from achieving full drop, none of the other hydraulics work. Most commonly for me, the arms get caught on some portion of the backhoe.
Option 2 is that the hydraulic pump sheared its teeth.
Option 3 is a loss of hydraulic fluid from a leak. If you don't have a hydro filter guard, that's the first place I'd look. A chafed hydraulic hose is another possibility.