iPhone 5 screws stuck?

I wanted to replace my iphone 5 housing, it was all going good untill some screws were not coming out. The screw on the top on the right of the vibrator, the screws holding the volume button and screw on the bottom right near the speaker. There was another one holding the flash and camera in place but i accidently broke that one. Please i need help as soon as possible. Take note that these screws are holding parts of the iphone together so i doubt that the screws are defective.