I followed exactly as in the video, but when I click nothing happens. Here's my code:
	public void update(GameContainer gc, StateBasedGame sbg, int delta) throws SlickException {

Input input = gc.getInput();
if(input.isMouseButtonDown(Input.MOUSE_LEFT_BUTTON)) {
sbg.enterState(0);
}
if(input.isMouseButtonDown(0)) {
sbg.enterState(0);
}
}

That's all the code that matters, but if you want my full code, here it is: http://hastebin.com/mirezohipi.java