Drilling is your last resort. Try hitting them with a hammer to try to bust them loose. Sometimes if you knock them a few times, it'll free them up. If that doesn't work, they have this tool that you put into the screw head (it has either a philips or flat head attachment) and you hit it with a hammer, and as you hit it, it turns. That sometimes helps for getting out really stuck screws. You may also try getting a variable speed drill with a reverse setting, set it to its highest torque setting, push down on it as hard as you can into the screw, and then push the trigger so it spins a SLOWLY as possible. If you do it to fast, you'll strip the life out of it. Try those three things if you can get your hands on the right tools. If none of them work, then use drilling as your last resort.