I would think if it takes two boots to get the audio to work it is not recognizing the driver on the first attempt. If the other suggestions are not the fix, maybe check the Device Manager to see what you show for sound. You may have one or more sound devices, but at least one should probably be an HD Audio and they should not have any yellow marks.
On my system, I load the Realtek drivers which also have their own control panel. If yours is not working correctly, you might want to check your manufacturer to see if any Windows 7 drivers are available.