Do you mean the disk is not recognized at all, or there are problems trying to access it, or you can access/view the disk, but can't read/copy anything off it?
Do you have access to a different computer you can try the DVD in, even just to see if it is readable? External optical drives can be finicky (though I have not tried any in few years).
Have you checked the computer or drive manufacturers' sites for updated firmware for your optical drives?
Are you shutting down all non-essential programs (especially anti-virus) inserting the DVD? Even with a software or driver conflict, I wouldn't expect the disk to be unrecognized, though.
You could try booting the computer into Safe Mode (hold the F5 key down while booting IIRC, or hit the F8 key for a boot menu), and see if the DVD is detected there.
You can return the game if there is a problem with the disk itself (even if they don't have any display systems there, they would have to have a computer somewhere in the store with an optical drive), and it is possible that store got a bad batch of DVDs. Statistically speaking, though, that isn't nearly as likely as a problem with your system. With a little troubleshooting on your part, hopefully you can either get it working, or have enough to convince Walmart to check the disk themselves; if they verify the DVD is unreadable, they can not refuse to take it back. A computer store probably would have checked the first DVD, before even doing an exchange.
