If you are having problems removing a seized screw and you need a little extra power. Tighten an adjustable wrench to the base of the screw driver. Pulling this at the same time will give you extra power behind your driver.
If the screw is rusted in position, treat it with a few drops of cola and try it again.
Treat the head of the screw with a few drops of hydrogen peroxide, allow a few moments for it to penetrate and the screw should undo easily.