I'm from China and My English is bad,so reply me if you don't know what I'm saying Yesterday when I'm watching some videos on my mid-2011 iMac it suddenly went black screen with no sounds. I waited for like 5 minutes and nothing changed. I pressed power button to let it reboot,and a grey screen appears after the apple logo and the spinning circle. Tried to do everything like safe mode,reset PRAM SMC,boot up from install disk,boot up from Recovery disk,etc. I can get into singleuser mode and repair disk,but nothing happens. I remember iMac mid-2011 has some graphic card issues and hard disk issues so I was wondering is it hardware problem or software problem. Anybody have same issue with mid-2011 iMac? Or also stuck in grey screen after the logo? Do you guys have any solution?Please tell me!