Jammed iphone 4s sleep button?

Well recently today, my iphone sleep button all of a sudden got hard to press down on. It hasn't been water damaged or cracked or dropped in that area. Does anyone know why this happens and how much a repair would cost? Thank you!

It's happened to me before, just keep pushing it down and try to get it pop back up. You can also use a toothpick or some other small needle to try and wedge it back up again. It happens and it will pop back up you just have to try some things to get it to do that. Good luck!