A non responsive laptop may need a PMU/SMC reset.
First unplug and take out the battery.
Next hold down the power button for at least 5 seconds.
Plug all back in and hit power again to turn on.
Mac Laptop Won't Start? Try Resetting the PMU or SMCCategories: Getting Help
I've been trying to get every last month out of my 6 year old 17" PowerBook G4 but it's been not starting for me lately. I've already had power issues when I cracked it open myself to do a repair and broke a connector. Whoops! So now the power will cut out if I press on it wrong when the power cord isn't connected. Not good.
Recently I couldn't get the PowerBook to crank to life even when plugged in when I wanted to setting up a presentation for my class. Fortunately one of my students came by and told me when it happened to him, the Genius at the Apple store unplugged his laptop, took out the battery and held the power button down for 10 seconds. After it was hooked back up it worked like a charm and so did mine when I tried it. Nice!
What I blindly did was reset my PowerBook's power manager. Since then I've looked it up on Apple's support site and found out you only need to hold the button for 5 seconds. This technique also works on most MacBooks and MacBook Pros as well, but it's called the System Management Controller (SMC). Late 2008 and 2009 models can do it with a key press sequence instead of taking the power away from the Mac. See Apple Portables: Resetting the System Management Controller (SMC) for details.
Also, don't forget MFM's Oh-No, My Mac Won't Start. Now What? for our take on the process of figuring out what might be wrong when your Mac is dead. This time I was lucky to have someone with the solution right at hand, but that's rarely the case.