Q: my mac pro wont start up - power cord is attached and green, start sounds are made but screen remains black

Problems related to startup, unexpected system sleep, shutdown, lights or fans call for an SMC reset:

Resetting the System Management Controller (SMC)

Resetting the SMC on Mac portables with a battery you can remove

1. Shut down the computer.
3. Disconnect the MagSafe power adapter from the computer, if it's connected.
5. Remove the battery (to remove the battery - click here: MacBook or MacBook Pro).
7. Press and hold the power button for 5 seconds.
9. Release the power button.
11. Reconnect the battery and MagSafe power adapter.
13. Press the power button to turn on the computer.

Resetting the SMC on portables with a battery you should not remove on your own

1. Shut down the computer.
3. Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.
5. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.
7. Release all the keys and the power button at the same time.
9. Press the power button to turn on the computer.