The screw holds a steel ball against a seat, maybe it didn't seat correctly, or there is some crud in there. I'd back it off, and try it again. It doesn't have to be very tight to seat properly, over tightening can damage parts in there.

Also, I have seen 1800s where if you throw the three point lever to fully raised from fully lowered too fast, they won't raise. This has to do with the linkage inside not getting repositioned during the lift, and a full raise while the arms are fully down will 'trick' it into sending a lower signal. If the arms were down and your lift lever was up when you turned the screw back in, this may have been what happened. Lower the lift lever all the way, and then with the tractor running, lift it in small increments. Once the arms have started lifting you should be fine.

Let us know if that doesn't help, and we can go on to other steps.