Q: how do i turn on my camera?

there is no on/off button, it starts when you open a program that requires it, like Photo Booth for example.  REad this: http://support.apple.com/kb/ht2090

Hope info from this article is helpful.

http://support.apple.com/kb/HT2090

Reset SMC.     http://support.apple.com/kb/HT3964

Choose the method for:

"Resetting SMC on portables with a battery you should not remove on your own".

If this does not help, contact Apple.

Best.