Cannot Play DVDs in Vista

I have installed K-Lite Codec Pack Standard 9.9.5 for Windows Media Player and Media Player Classic on 3 different Vista Computers. On all 3 computers, both Media players will play any video file. However, when I insert a DVD Movie disk in any of the 3 computers, Windows Media Players reports it cannot play DVD Movies, and Media Player Classic reports "opening" then just sits there for ever without progressing further. If I install a third party player e.g. KMPlayer, DVD Movies play normally in the third party player. I have tried the solutions in the FAQ and re-installing the K-Lite package several times without success. Any ideas?

I don't have any Vista system nearby to test. You could try selecting ffdshow as MPEG-2 decoder. Or the internal MPEG-2 decoder in Media Player Classic.

Thank you - I have already tried ffdshow with no effect on the problem. Yes, I could use Media Player Classic MPEG-2 decoder, but i really want to know what the problem is with the K-Lite codecs. Does any one else (with a Vista system) have any ideas?