So it all began today when I started up the computer.
The Windows 7 Aero theme is behaving really weird. All the window-borders are gone, and the shadows are really weird as well. The semi-transparent border is still there, but the small black border around that is gone too.
The minimize/maximize/close buttons are not good either.
Actually, just look at this image and you'll see:
If I set the theme to Windows Classic and then switch back to Aero it looks fine again, but it switches back to this weird look after a while by itself.
Any ideas what might be wrong?