I just upgraded memory in my mac book pro to 4 gigs. Now it won't start. It is as though the power switch doesn't work - because the little light does not come on, and there is no start up sound. I have tried replacing the new memory with the old memory and nothing happens. I have tries it with AC only - no battery- nothing... And I have tried it with the battery (which is pretty much charged - 4 of the 5 green lights are glowing - the 5th one is blinking). What could I have done to mess it up?