Windows ride video "white screen" on start

since january i have a problem with fulgaz. i did an update then which did not work well. I had to reinstall fulgaz. i also got the message to install .net desktop runtime first. i can open fulgaz without problems. i can download a ride without problems. i can connect my tacx flux s without problems. BUT, when i want to ride a ride and i press start i get a blurry yellow screen with hud and the countdown "set" and "go", but nothing happens.