anti-aliasing = blackout

I was trying to get some good screenies of my character the other day, and to improve the image quality I turned the anti-aliasing up from 0 to 4X. Some odd screen phenomenas occurred, like I couldnt move properly and a shadow of a character kept showing up upside-down on the left side of the screen. Really quite weird.
I turned down the anti-aliasing from 4X to 2X, then I couldnt open my inventory, but the rest worked OK. I took some screens and had a look at them afterwards... they were black. Just black squares.

Also, when I ignore the anti-aliasing and just turn the graphics quality to max, everything works fine in-game, but when I look at the screenies afterwards they're really crappy quality.

Why is this? What can I do about it?

Likely that your graphics card can't handle AA - that, or drivers are wigging out, so the game goes bonkers.

What is your computer's specs? It would help a lot to determine the problem.