IPhone 4S screen frozen details below?

So I have an iPhone 4S that I've had since December 2012 and today I was doing something with the settings (nothing big just changing the wallpaper) and now the screen is stuck on the settings but it still moves and stuff it just won't go to the home screen or turn off I have tried assistive touch and that didn't work I don't want to get it fixed at the apple store coz it will be expensive and time consuming but if worse comes to worse ill go. K thanks bye (:

Added (1). Also when it's meant to automatically go off the brightness just goes down
And I plugged it in and it's charging and everything it just won't go off the settings screen

My screen often freezes or just black outs. Mostly when I press the buttons to screenshot it'll presume normally. But sometimes it may take a few screenshots till it does.

Hold the same buttons for screenshot down until the phone shuts down, it is just like holding the power down on your computer. Reboot and hopefully your iPhone is fixed.