@lodidoesstuff start with something like this:
Resetting the System Management Controller (SMC)
The System Management Controller (SMC) is a chip on the logic board that controls all power functions. If the computer is experiencing any power issue, such as not starting up, not displaying video, sleep issues, or fan noise issues, resetting SMC may resolve it. To reset SMC:
1. If computer is on, turn it off by choosing Shut Down from the Apple () menu.
2. Connect power adapter to computer and to a working power source.
3. On built-in keyboard, press (left-side) Shift-Control-Option along with power button just once. Important: Use Shift-Control-Option keys on left side of keyboard.
Note: When the LED on the MagSafe connector is orange/amber, resetting the SMC will change it to green for a few seconds, indicating that SMC was correctly reset.
4. Wait 5 seconds and press power button to start computer. Note: If bottom case is removed, you can alternately reset SMC by disconnecting both power adapter and main battery, and holding down power button for 5 seconds.