I would try to reset the pram and smc first (even if it might not be 100% nescessary - it would rule some settings issues out)

PRAM and NVRAM reset:

1. Shut down the computer.

2. Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.

3. Turn on the computer.

4. Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.

5. Hold the keys down until the computer restarts and you hear the startup sound for the second time.

6. Release the keys.

SMC reset:

1. Shut down the computer.

2. Plug in the MagSafe power adapter to a power source, connecting it to the Mac if its not already connected.

3. On the built-in keyboard, press the (left side) Shift-Control-Option keys and the power button at the same time.

4. Release all the keys and the power button at the same time.

5. Press the power button to turn on the computer.

Note: The LED on the MagSafe power adapter does not change states or temporarily turn-off when you reset the SMC.

I had this problem with my Macbook running 10.6.8, audio okay but nothing visible except a black screen. The SMC reset was all that was needed to bring things back to normal.

Thanks!