I have an Early 2011 MacBook Pro (A1286). I upgraded it to macOS High Sierra and I sold it to a friend of mine, who returned it back after few weeks because it stopped booting. It always gets stuck at white screen after the loading bar reached certain level, no matter what booting method we tried - safe mode, recovery, recovery from the Internet.
After few days of several attempts, I had a bad idea of downgrading firmware by using the Firmware Restoration CD 1.9 which was probably not intended to be used with the particular model. At first, the CD did not do anything during booting but I forgot it in the DVD drive. However later during one of reboots, the laptop beeped and probably installed the firmware. Since then, the keyboard does not work and of course, it still does not boot.
Is there any way, how to repair it and install the correct firmware?
This is probably not related to firmware but some hardware error. I removed the hard drive and installed Sierra on it from different Mac. It still hangs with a white screen.
UPDATE 2: USBs seem to be dead as well. External keyboard does not work and even the LED indicators do not switch on. The same for infrared mouse which does not light on. Arduino works gets power from the port. Nothing from the USB boots even though it did before.
I also tried a hard drive with Ubuntu which booted before. The screen goes black and stays like that.
I haven't tried CD/DVD as I don't have an option how to eject it then. I even had a problem to remove the Firmware Restoration CD. I had to use a very brute force to get it out.
UPDATE 3 (as of 2018-05-03): I have tried to boot latest Ubuntu from DVD. The system probably booted as the DVD device was working for several minutes. This time, all I could see was just a black screen. A GPU issue? But I don't know why the keyboard is not working :-/
UPDATE 4: An Apple service identified a hardware problem on a main board, which would need a replacement. Thank you all for your advices.