My 27" iMac came back from the local apple repair agent yesterday having had the video card replaced to cure a white screen issue. It booted up once but on booting up this morning the white screen is back and what's worse it no longer responds to any inputs from the USB keyboard so I cannot access any recovery options. I have tried unplugging all connections including power lead and leaving it for ten minutes but no change. I am very disappointed with this iMac. I thought I was buying a quality product from a quality manufacturer. It is only eighteen months old and has been to the workshop twice already. The quality control on the unit has to be suspect. I have windows pcs that are five years old and still going strong. Sorry for the rant but I'm really annoyed with Apple.