Hi, I'm stumped. I'm dealing with a screen (mid-2010 iMac 21.5, 10.6.8) that black out on me all the time. Shine a flashlight on it, can see stuff, so it seems like the backlight is going out. External monitor works. If watching video sound still plays. This is happening from every few seconds to every few minutes. I use a hot corner or the keyboard display sleep command to bring it back but it goes right back out. It'll happen at the gray startup screen before the Apple logo or later during use. The LCD has been replaced already. Hardware or software issue? This does not happen running bootcamp (XP SP2). I booted from my OS X install disk and it blacks out, making a reinstall almost impossible. This part I don't understand at all- why does Windows work but not the OS X install disk? The intermittent nature of the problem plus uncertainty if it's hardware makes me want to figure it out before bringing it back in for repair. Any thoughts? Thanks!