I have a 24-inch iMac (2.8 GHz Intel Core 2 Duo) running version 10.5.8 software. The question is: How do I temporarily disable the start-up sound when turning on the computer. I notice that the volume at start-up relates directly to the previous setting when shut down. Sometimes, however, silence is needed when starting up. Is there a key I can hold down during start-up to do this? Thanks so much!