That could be several things...
going on, but I suggest:
1. Make sure it's plugged in.
2. Press the Power button and hold down the Command button, Option button, P button, and the R button at the same time, until you hear the Startup Sound a 2nd time, release and you should be good to go. This resets your PRAM or your perameter RAM.
3. You can also disconnect the power adapter, remove the battery and holding down the power button for at least 5 seconds, this resets the computer to its factory settings.
If these fail, check with Apple Support over the phone or stop-by the nearest Apple Store. Good Luck.