Jammed lock screen button
Like Alan said, go to a repair shop or an Apple store and ask tell them what is wrong. I wouldn't take it apart yourself as you may damage it, unless you have experience with repairing stuff. To my knowledge, there really isn't an 'easy' way to fix it. If you want to try it yourself, here is a tutorial: http://www.imore.com/how-diy-repair-stuck-or-broken-iphone-4s-power-button