WMP 11 and DVD's

I'm sure this has been asked and answered before. WMP11 won't play a DVD. Under play, DVD/CD is grayed out. The NVIDIA decoder was loaded and the Microsoft Decoder tool indicated that it was the right program (but for WMP10--no info provided for WMP11.) The DVD (Optiarc DVD AD-5170A) will play music, but it doesn't even show me the files on the DVD disk. Could it be the driver? I am about to reinstall the NVIDIA program. Is there something else to do first. BTW: though I have requested Autoplay, the DVD doesn't automatically run it.

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