Gray screen after boot and blue screen with stripes

Question

Hi, I have a MacBook Pro Mid 2011 with Mavericks (came with Snow Leopard).
History:
One day i was working and things were too slow. I tried to restart but it was taking too long to close all the programs. So I forced shut down by holding the power button. When I turned it on again, my problems begin.
Problem:
The Apple logo and the spinning wheel appear. After a while, both disappear and it freezes at gray screen. Some solutions I tried make the screen goes blue with black vertical stripes. In both cases, I have to force shut down.
Solutions I tried:
- Reset NVRAM
     It does reset, but nothing change
- Log in my Windows partition. I can't log
- Hold option key and choose recovery. Blue screen
- Recovery system by restart and press Command-R. Blue Screen.
- Safe boot by pressing Shift. Blue Screen
- Verbose by pressing Command-V. Restart and gray screen again.
- Single-user mode by pressing Command-S
     Tried to reapair hard drive:
          /sbin/fsck –fy
     Returns the message "** The volume Macintosh HD appears to be OK.". I restart and nothing change.
     Tried to change startup permissions:
          mount -uw /
          chown root /
          chmod 1775 /
          exit
     Restart and nothing change.
- Boot from a bootable USB flash drive
     Holding option key, I choose my flash drive with Ubuntu installed. It gives me 3 options: Use Ubuntu without installing, Install Ubuntu, Repair Disk      Errors (something like that). The 3 options go to the blue screen
     Flash drive with Mavericks. Blue screen.
-Boot from my Snow Leopard CD. Gray screen, restarting, gray screen.
I don't what else I can do. Is it a hardware problem? At first I thought it was some corrupted file. But is it a GPU or logic board problem? What else can I try?

Answer 1

I found this to work at least to get in and backup some files. It is VERY important to put these commands in EXACTLY as seen here, including spaces.
Boot into Single-User mode (Command-S while booting up)
Execute the following commands:
/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
I guess these two graphics extensions go bad quite often on Macbook Pro 15-inch.  They are part of the logic board. The only problem I had was I still couldn't get into my computer any other way, and the graphics for Safari were messed up.  Firefox was okay.  Good Luck!
Here's the original thread:
http://apple.stackexchange.com/questions/120507/boot-hangs-on-grey-screen-even-w hen-booting-from-usb-drive-with-fresh-os-x-inst