What usually caused this glitch?

In Dragon Age origins, I have this glitch where my character just walks right into the terrain, and the paths etc that I'm supposed to walk on top of, I'm underneath them instead looking up. In other words, nothing is solid. I don't even know why this glitch happens or what it's called. I posted a pic of it in another thread but I didn't really get a response......probably because, like this one, I found the question hard to ask and the problem hard to describe. Does anyone have any idea why this might happen? All drivers are updated and temps are normal. Thanks in advance!