My Unibody MacBook Pro '2.53 Core 2 Duo 4GB RAM', has an intermittent issue with booting up. It seems to power up, but hold on black screen and sometimes never get to the grey screen. I can turn the machine off again immediately just by pressing the power button once. PRAM reset doesn't always work. SMC reset doesn't always work either. This happens when the battery is both charged, or low on juice. My machine has already been off under AppleCare where the authorised repair centre failed to find a problem... http://www.youtube.com/watch?v=bsqZfi-_1Y0 Any suggestions? Another issue with my MacBook Pro in which the sound sometimes disappears upon startup or wake from sleep. This sometimes occurs after the 'boot up' issue. Here is a video where I've lost the ability to alter the sound. http://www.youtube.com/watch?v=dwaXr8H6qzc I'm totally frustrated and confused as to what could be the problem. After sending it off once, and it being returned 'flawless'... I decided to shoot these videos to prove that there is an issue. Thanks in advance... I really appreciate any time taken watching these videos.