What could have happened,
Was the plastic "Rod" which leads from the handle to the inner switch has busted, this has happened before to me once, one a Twin-Chamber machine. I believe these parts are N.O.A (No Longer Available), but if your lucky your local shop may have one.
It may be a pain to replace, but you could always just rip out the busted rod and do it the "Quick-N-Dirty" way of flipping the internal switch and wiring a in-cord switch onto the cord. We did this years ago, to a Fantom Thunder.
(By the way, "Rip" and "Hoover" should never be in the same sentence,
-Alex.