I’ve got a Mid 2011 27” iMac and about 5 months ago I booted it up and I didn’t see anything on the screen. I could hear the startup chime but the screen was blank. At first I thought it just wasn’t booting but latter I stumbled onto the fact that it was. I logged in to Teamviewer which was running on the iMac. I saw that it was running so I logged in and everything was running like normal. I suspected the monitor at first so the next thing I did was to connect a mini display adapter and connect an external monitor still nothing. At that point I’m thinking it’s the videocard because shouldn’t the external monitor work if the internal panel is toast? I’ve been using it via Teamviewer but it seems like such a waste. I took it to a Genius Bar but they couldn’t tell me definitively what it was. I can’t remember exactly but I think they said they would replace the videocard for $500 and if it still has the problem then they would replace something else. I don’t really want to pay $500 just on the chance it might work.