From your description it sounds like you adjusted the worm shaft preload. That adjustment seldom needs to be touched after initial set-up. It is possible by over tightening that adjustment you could have broken the thrust bearings????
The only adjustment that is most commonly needed is on the three bolt side cover. It has a lock nut and the adjustment is done with a screw driver in the end of the bolt.
I would do as suggested and look at the rest of the components first.
