Hi,
This is a Mac mini (Mid 2011) Core i7 with AMD Radeon HD 6630M. It was working fine with macOS Sierra until it was updated to High Sierra. After the update fails to finish boot, shows Apple logo and then goes to the 'white screen of death'. I did try about all the things I found on internet that are basically shown here
eshop.macsales.com
I also erased the hard disk and did install several different macOS (10.8; 10.11) but still hangs on the white screen. Booting from USB didn't work either. Before erasing its internal hard disk and SSD, Windows (alone on the internal hard disk) didn't boot. Is this a hardware failure?? Any other ideas? The Mac mini passed the Apple hardware test (3A225) I was able to do online.

This is a Mac mini (Mid 2011) Core i7 with AMD Radeon HD 6630M. It was working fine with macOS Sierra until it was updated to High Sierra. After the update fails to finish boot, shows Apple logo and then goes to the 'white screen of death'. I did try about all the things I found on internet that are basically shown here

Recover From the Dreaded White Screen of Death When Booting a Mac
From time to time, you may experience one of the more frustrating Mac glitches – the "white screen of death" during boot. Here's what you can do about it!

I also erased the hard disk and did install several different macOS (10.8; 10.11) but still hangs on the white screen. Booting from USB didn't work either. Before erasing its internal hard disk and SSD, Windows (alone on the internal hard disk) didn't boot. Is this a hardware failure?? Any other ideas? The Mac mini passed the Apple hardware test (3A225) I was able to do online.
