iMac 27" mid 2011 black screen The Mac starts up and runs probably on thunderbolt to vga adapter but the built in screen remains black. It has an AMD HD 6770m graphics card so not the one under the repair program. 
Any ideas what could be the problem?
Another possibility is your backlight may have gone bad.  You can check by holding a flashlight up to the display and looking closely.  If you can see the icons on your desktop once illuminated with the flashlight then your backlight is out.  This is a relatively simple repair you can have done at the Apple Store.