Disassembly is pretty simple.
1. Use a small screwdriver to push the 4 little rubber pads out of their holes.
2. Unscrew the four small Phillips head screws underneath.
3. Use a fingernail or something thin and flat to get leverage under the edge of the back panel and carefully pull it off the unit. The panels clip together, so there will be some resistance. Be careful of the ground wire near the L button.
Here is a picture of the inside. I zoomed in on the power switch for you. Sorry about the resolution, this is from months ago, and I didn't think to make a close-up of the power switch. You can see how the outside switch fits around a tiny little switch inside.
As far as I can tell, one of two things has happened:
1) The outer switch has come apart from the inner one.
-This can be solved by simply putting it back in place.
2) The inner switch has snapped.
-To fix this would either require some incredibly delicate gluing, or finding an appropriate switch to replace it with.
Unfortunately, I think the second is more likely.