Candy, you'd written earlier that you'd clicked on RESET TO DEFAULTS but I wasn't sure if you and I were using the same control panel screen - that's why I use precise names.
You mentioned the VOBs were file-associated to one product but, actually, DVD players look for a file called VIDEO_TS.IFO as their "start up and control services" activation for all Video-DVDs. This is a small file that is basically, "Start here, and here's what to expect, and there's the Step 2 file to play now..."
Associating to a VOB file gets me the Movie to play, but that's not quite the same as "getting the DVD to play". To load menus, display opening screens, and what sequence of videos is presented.
If I associate my VIDEO_TS.IFO file (found in any Video-DVD's \VIDEO_TS subfolder) with a DVD player, then I'm "playing the DVD" not just the VOB Movie File.
As for the suggestion of adding another driver, Candy, I'd agree with you. This sounds like a Conflict and adding another driver (like AnyDVD is) might not be clearing up muddy-waters but adding to it.
It reads like you've got six DVD-Player possibilities there (including iTunes) and IF I had the ability to reinstall some (or all) of those, then I'd start uninstalling those first. And do a Restart, and each time run a Test Play.
I have a feeling you're dealing with a Conflict here, and trying to eliminate the software that's clogging up the mix could be more hairpulling than a forum test of nerves and typing precision.