Start-up Repair or System Restore
Insert the Vista Installation DVD and press a key to Boot at start-up. It should display a prompt that you have an existing operating system on your PC. Wait for the application to load files, which can take some time.
Once the screen is up, choose your language, time and currency and any other options. Click next and after the program has found the existing installation, select your operating system (Vista in this case) and click next.
Now recovery options will come up (Start-up Repair, System Restore, Complete Restore etc.) Choose either the ‘Start-up Repair’ or ‘System Restore’ option and the process is fairly intuitive from here on in. You can choose whether to shut-down your computer or restart after this process (restart recommended.)
The recovery program will look for any corrupt files and attempt to repair them accordingly. It will show a report at the end and you can restart your computer to see if Media player is now working.
This remains the surest way to resolve problems related to the player. Users have tried to uninstall the program, or re-install it by downloading a version from the Windows’ website. This method is not recommended by Microsoft and will likely cause further problems, even if it seems successful.
You can also look at the following resources in case you have other problems with the player, and which have proven particularly useful in solving specific problems (such as streaming content) related to the version bundled with Vista.
Windows user group network
Windows' client tech centre
Tip & Trick.net
For more on Windows Media Player read Bright Hub's Collection of Windows Media Player Tips, Tricks and Tutorials and Installing Windows Media Player.