There are several things it may be. Look at the trouble shooting page since there are multiple options included there.

If you damage or lose screws and/or the black electrical tape you will be able to find replacements at a hardware store.

If you take the back cover off again, as well as take out the circuit board, you will have access to the stuck button. Push the button back into place. Replace the board and cover and your camera should be ready to use.