My iMac won't get past grey screen, I've tried holding down c. I've tried holding cmd+s. I've reset my PRAM etc, I've put back in RAM it came with, and when I turn it on I just get grey screen, apple logo and the spinning thing! Updated it to new snow leopard OSX 10.6.6 and it has a DVD in the drive and I can't even get that out! What can I do???