In case thats the cause of your problems, you might find this topic helpful:
Unfortunately I haven’t found a video or pictures on how to change the buttons.
But it’s not to difficult, if you have some patience, a steady hand and can work with tweezers or the like:
The buttons are fixed like this.
- Take off the buttons (camera and power) by gently removing the transparent rubbery strip from the black pins (it works like a press stud/snap fastener).
- Take the power button (the surface is ridged) and put it in on the place of the camera button. Take care to place it correctly, the rounded side goes into the back cover. (It can be done the other way around; believe me, I’ve been there accidentally
. You realise your error, as soon, as you try to attach the cover to the phone again. Then you’ll have to do it again. 
) Place the holes in the transparent rubbery strip over the black pins and use tweezers or maybe the tip of a ballpoint to push it into place. Do not use to sharp an object, as you don’t want to damage the rubbery part, because that might result in cutting it and you needing to buy a new slim cover (buttons are not sold seperately as far as I know) - Take the camera button (the one with the smooth surface) and fix it the same way in place where the power button was before. Take care of the orientation of the button as well. It’s the same: rounded side into the cover.