A screw can become seized in the object that it was driven into. This means that traditional tools used to drive in the screw will no longer take the screw back out. The screw will not budge, and continued attempts to remove it only make the situation worse. All is not lost when dealing with a seized screw; there are methods available that will break the screw free so you can remove it.
Drill a hole in the centre of the seized screw with a centre cut drill bit for metal. The bit that you use should be at least one size smaller than the head of the screw. Drill the hole no more than 3/8-inch deep.
Place the tip of an appropriate sized screw extractor into the hole you drilled. Tap the square head of the screw extractor with a hammer. Striking the head of the screw extractor will drive the tip into the hole you drilled.
Place the tap handle onto the head of the screw extractor. In the centre of the tap handle is a square hole. The square hole will slide over the square head of the extractor.
Slowly turn the tap handle counterclockwise (or to the left) to back out the seized screw. Continue turning the tap handle until you can remove the screw.
There are extractor bits available that can be used in a variable speed drill. This type of extractor does not require that you drill a hole in the screw head first. The bit is inserted into the drill, and then the drill is set to rotate in reverse.