Ever since I updated to High Sierra I've had tons of video problems that include black screens and flickering menus. I disabled DirectX and now everything looks like crap.
I made a video showing what's going on. https://www.dropbox.com/s/9wbyc0g5hbe4l92/2015.mov?dl=0 It does it when using 'Best for Retina display' and 'Best for external displays'. I'm currently using my macbook display and two external displays. I'm also uploading a screenshot of my Graphics settings in Parallels.
Here's another video where the display became unresponsive: https://www.dropbox.com/s/w0b9hhn0ewx2q8v/Unresponsive.mov?dl=0 I'm also including a screenshot with my settings again. I tried it with display mode switching turned off. So far the only thing that works is turning off DirectX.
Please take a snapshot, shut down Windows, select the option 'Scaled' (just for test purposes - this option may make you compromise on video quality in Windows) in virtual machine configuration under Hardware -> Graphics -> Resolution, enable 'DirectX 10', close the window and start up Windows. Let us know if the issue persists.