Screen bug on windows 10 on iMac Hi I tried to install Windows 10 as dual boot on my iMac (late 2009) High Sierra. First I ran into this problem someone else also had here, which is unfortunately unanswered. Anyway since I couldn't use Boot Camp Assistant, I created a bootable usb stick and installed windows manually. This worked quite well.

Then when my screen went sleeping because of I was afk for too long and I woke him up suddenly the screen split into 4 parts like in the image:


So I reinstalled windows 10 but they same happened, when the screen went to sleep (restarting didn't restore normal screen).

What can I do? Does this sound like a windows problem? Or is it due the fact that I am booting it on a Mac? Is there hardware incompatibility? I mean it works fine until the screen goes sleeping. I could reinstall windows and turn off screen sleeping as fast as possible but then something will possibly trigger this again.

edit
When I restart on macOS then there stays a line from this bug which disappears after the login
this seems like a software issue. Once you are booted into macOS, try reinstalling Windows support software from Apple via BootCamp. Once it is downloaded, install it to your Windows partition. Check this out for installation help: https://support.apple.com/en-us/HT204923

The problem with doing a manual install Is that it doesn't always install necessary drivers. 

If the problem continues, then try doing a power on self-test. To do this, reboot the Mac and hold "D" while it is starting up.

Good luck!