Which screw was it? The ones in the plate or the needle? The needle one I use my rubber gripper from the kitchen to loosen it if it is stuck. The screws on the plate you could put a drop of machine oil on them and wait a few minutes to try again. If still stuck and you need to get in there, I think a visit to the repair shop might be in your future. If you don't need to get in there, run your machine for a while. I find that the vibration of the machine sometimes loosens the screws.