It sounds like the striker block spring is not properly aligned. Sometimes they get bent when you are sliding the sight back on. You should always push the striker block in a few times after messing with that spring to be sure that it is functioning.
My suggestion would be to remove the sight and see if you can remove the striker block. If not, can you lock the slide back? If so, plan B would be to lock it back and remove the slide end cap and then remove the striker assembly. The slide should come off.