Sounds like a video card/driver problem. Make sure you have the latest updates.
Could be what Curt said... You have changed something in your graphics setup and it's wreaking havoc with the file dialogs. Likewise, you may have changed your default Explorer folder view to something that wasn't supported back then. File dialogs are more or less just a special flavor of Explorer windows and inherit these settings, so if you e.g. chose thumbnail view and PS6 can't handle it, welll *kaboom*...
If what the guys above have suggested don't help, you might want to clear your preferences and return Photoshop to its default configuration: Press and hold Control-Shift-Alt when cold-starting Photoshop. If you're quick enough (and you have to be VERY quick), it will prompt you to delete the current preferences.