I've had problems with MacBook Pro some time ago - screen went black screen (probably GPU problems as there are lots of complains on the internet fitting my problem) and after that I couldn't boot with any mode at all except for Single-User Mode (CMD+S). I would get either grey or blue screens.
Specs: MacBook Pro 15" Early 2011, i7 2Ghz, AMD Radeon 6490M, Mountain Lion OS X
The only solution that helped me to boot again was this:
/sbin/fsck -fy / /sbin/mount -uw / mkdir /Disabled_System_Library_Extensions cd /Disabled_System_Library_Extensions mv /System/Library/Extensions/ATI* . mv /System/Library/Extensions/AMD* . touch /System/Library/Extensions exit
After that I've tried to install Yosemite OS X - thought that maybe clean install will help. I've gone with the installer I've downloaded from App Store, started it, laptop rebooted after a while (which is normal for OS X installation), then went grey screen again and nothing happened after that.
Now I'm trying to start with Single-User mode but it goes directly into Installer partition.
Booting with Alt/Opt doesn't help - I can only see OSXInstaller partition and Recovery disk (which goes blue screen if I select it).
Is there a way to force MacBook Pro boot into your installed OS X avoiding Installer?