Mine has been adjusted and trouble free for years now so I am admittingly a little rusty on what that screw is actually doing. I'd try to find a schematic at the Hatsan site or the manual. I just checked and I don't even have a manual for it either. Sorry. I can't say anything that isn't a guess at this point. Good luck.
Wait a second, I thought that set screw was on the hammer and the hammer adustment from the back was inside of it and the set screw went through to hold the screw you were turning? Turn the adjustment screw back in all the way, tighten the set screw and try cocking it and fire it again. If it works then adjust it. I'm going from a bad memory here but if it is something other than that , you might have to call Hatsan customer support if you don't find it in a faq on their website.