Hi Paul,
I'm assuming it worked before you adjusted the screws, so I can only suggest that you pick one screw only and adjust it 1/2 turn at a time until the screen stops without you pressing the 'stop' button. With my new Beamax the lowering adjustment is the screw towards the rear of the case (though it does say in the instructions that it can vary depending on whether the screen drops from the front or back of the case). Mine drops from the back of the case for reference. Clockwise adjustment raises the drop point (which seems to be what you're after) on my Beamax.
My only concern is that you may have adjusted the screw beyond the limit of it's travel, or the microswitches have become dislodged. In this case you will need to remove the screen from your pelmet. Hopefully it won't come to that (I struggled to install mine recently in a pelmet that I'd built for my previous screen, so I feel your pain

).