What is happening to my level?

I started using UE4 a week ago and i had no problems with this. But i don’t know what is happening to my computer that after a while Open GL stops working and i can’t play any games, so i opened UE and suddenly my level stopped working correctly and now it looks weird (see the image).
I restarted the computer and it still looks the same, so is there any way i can fix this?

try reinstall unreal engine