The first thing that comes to mind is your keyboard to logic board connection. Make sure it's seated. Next reset the the SMC (power setting), here's how:
• Shut down the computer.
• Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
• On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
• Release all the keys and the power button at the same time.
• Press the power button to turn on the computer. Note: The LED on the MagSafe power adapter doesn’t change states or temporarily turn-off when you reset the SMC.