Pixel grid over images

Photoshop is putting a heavy grid on top of my images, making it very difficult to work with them. If I save them, though, they appear nicely in Lightroom or other photo viewers. I did uncheck "Use Graphics Processor" in Preferences/Performance, and restarted the program but the problem persists. Here's a screenshot. I'm new to Photoshop and have no idea what's causing this.