A lots of people complaining about Discreate Graphics Card Issue on theirs MAcbook Pro’s from 2011. Here you can find information about the problem: https://discussions.apple.com/thread/4766577 . Currently I have the same problem and event cannot use gfxCardStatus to switch to Integrated card.
I did some research and find probably the way how to fix it. here is an instruction for every one who cannot boot even to safe mode:
How to switch to Integrated Intel HD graphics card without using gfxCardStatus – BETA – still under tests !!!
1. Reboot Mac and enter to the Console mode (Command + S before gray screen appear)
2. mount -uw /
3. create folder example /_temp
4. move ale AMD folders (files) to folder you created
sudo mv /System/Library/Extensions/AMD*.* /_temp
!!!! 5. Execute command:
sudo kextcache -v 1 -m /System/Library/Caches/com.apple.kext.caches/Startup/Extensions.mkext /System/Library/Extensions/
This will rebuild kexts cache which won’t contain AMD drivers kexts
6. restart your Mac using – sudo reboot
7. Start your Mac normally – Mac should use only Integrated Graphics Card now
!!!!!! PLEASE REMEMBER – THIS IS BETA FIX – STILL UNDER TESTS !!!!