Dvd decoder. I am having problem running my window media player [latest version]. An error message

Question

I am having problem running my window media player [latest version]. An error message stating it has problem with the dvd decoder. I have even tried installing other dvd players such as amazing dvd, power dvd but the same problem [message] came out. For your information I am using window vista home basic and one more thing , I would be very glad if you could help me on how to install dvd decoder.[step by step instructions]