Mac OS does not boot on Imac, but Windows does. Mac OS won't install, how to install Mac OS?

Question

Iron

Welcome all!
I have been looking for an answer and a solution to my question for more than one evening, to no avail.
So, introduction.
Imac 27 inch 2011. Processor I5 3.1, AMD Radeon HD 6970M video, 12GB RAM.
1 hard HDD per terabyte, second SSD 128 GB. I installed the SSD drive and the system on it myself about a year ago.
Mac OS Sierra was on the second disk (SSD), the machine flew and worked flawlessly.
On one not the most successful day, a white screen appeared during work, an emergency shutdown.
And after that things started to happen. Restoration via the Internet - does not work. Booting in safe mode - does not work. Hardware test from Apple does not find any errors on detailed testing. White screen when turned on.
The first thing that came to mind was the SSD. I read many times that they do not live long. After reading the forums, I began to lean towards a problem with the video card. I also read that it was these poppies (27 inches of 2011) sold in the first year that were defective video cards and Apple even changed video cards for free (the last 4 letters of the problematic series are indicated, just coincided with my poppy). I removed the SSD, connected it to a Windows computer, the data is intact, copied what was needed. There is no original disk with a native system for Mac, I pumped up 5 pieces, not from a flash drive, not from a disk, the system is not installed. There were various errors when trying to install Mac OS.
I can list further actions in the wrong order, since I have already dismantled the poppy 10 times. I turn on only from the HDD and the recovery via the Internet works. I install the original LION axis on my native Makovsky HDD and everything seems to be going well, but after a reboot during the installation process again a white screen. But booted into safe mode and finished the installation, he still turned on. I noticed that the windows appear in a cascade and more and more inclined to a problem with the video card. After copying all the data from the HDD, I rebooted to exit safe mode. After the reboot - a white screen and no longer in the usual safe mode does not turn on.
I removed all 4 sticks of RAM and turned on each one individually. On some there were 3 long beeps that indicate a problem bar, removed the bar.
I put the SSD back and again, through the Internet recovery, I put the LION axis on the SSD and again after rebooting and choosing to boot from the SSD, a white screen. Again I complete the download successfully in safe mode. And again a white screen and it does not boot in normal, not in safe mode.
After re-reading a bunch of garbage on the Internet, I nevertheless inclined to believe that the problem is in the video card. There is no desire to bake in the oven according to the advice of many.
But what was my surprise today when I removed both disks from the poppy and installed only one old HDD with Windows Enterprise and it turned on and works. About 5 drivers are missing, but it works!!! Then there can be no problems with the video card - the first thought.
Really in a native disk HDD business? Both HDD and SSD work when connected to a computer via a USB adapter.
At some point, the error was something like Device in slot: SLOT-1 googled that it was connected with the video card.
Now again I will shovel the entire Internet with new nuances. The big news for me is that the Mac worked with Windows, but I don’t want to have a 27-inch Mac and Windows inside, Windows in my Mac was already in a virtual machine.
I would be sooo grateful and grateful to connoisseurs and experienced users of poppies for ideas, advice, tips!
Even for reading to the end of my story - thanks already !!!
PS If this is still a video card, then can someone tell me links to stores with delivery in Europe to buy such a video card? I find only on Ebay at some dumb sellers.

Answer 1

Run something on Windows that will load the video card. By themselves, Win and Mac interact differently with the video card. Also, it is advisable to install a driver for the video card to be sure that Windows can use it to the fullest.
PS My opinion: it's still a card. The fact that it works on Win does not mean that everything is ok with it.