There is no means to remove the dedicated graphics logic as its part of the logic board.
More often the HD and/or the HD SATA cable need attention.
If you do have a GPU issue then you'll need to get the logic board repaired. A major issue was the capacitors breaking down due to heat.
During the boot up process the system is using the low res graphics within the GPU services (Intel HD Graphics 3000 and/or the dedicated AMD Radion). So the fact you see horizontal lines on screen implies either the CPU has a problem or the display does. Hopefully you can use an external monitor to see if the lines are visible their.
A blank white screen is indicative of the either a hardware or OS level problem. Basically the system was unable to get past the Power On Self Test (POST) process.
Reference for the next steps: Startup key combinations for Mac
- The first thing I would do is restart the system in single user mode to see if the system is able to process the OS Start up your Mac in single-user mode or verbose mode. As this is a command line interface the low res CPU graphic services will be used. Did it run thought without any errors? If you see an error carefully note the complete line.
- The next would re-start in Safe Mode: Use safe mode to isolate issues with your Mac. Safe Mode also uses the low res CPU graphic services.
- Next I would run Disk Utility to make sure the drive was OK. If you encounter any errors here you may need to reformat the drive and the HD SATA cable could be bad (pop the cover off and check the black plastic bottom cover clips along the mid plane wall the one near the HD is important! If its broken you'll need to replace it with the good one on the other side if its OK, otherwise you'll need to find a replacement set and replace the SATA cable. You might want to also try booting up under an external drive.
If all of the testing so far goes through without any errors then you likely have the bad capacitor issue. You'll need to find someone with the skills and parts to replace them.
Let us know what you find.
From your latest testing I'm sorry your logic board needs some serious TLC here.
As an option have you looked at just replacing it? That might be a cheaper & faster option MacBook Pro 15" Unibody (Late 2011) 2.4 GHz Logic Board - Used, here's the IFIXIT guide you'll need to follow: MacBook Pro 15" Unibody Late 2011 Logic Board Replacement