Hi there,
It might be a software issue, a problem that has been haunting Apple for a long time now.
What you can try (and make sure you follow the steps as explained) is this:
-Power down your macbook
-Remove the magsafe connector
-Remove the battery
-Hold your power button in for at least 5 sec
-Reconnect the magsafe connector
-Wait till the magsafe turns green
-Wait at least 5 sec
-Put the battery back in
-Start the macbook
Let me know if it helps or we can try other solutions.