Network Discovery will not turn on

Hello everyone. I appreciate any and all help anyone might have for this
issue. It is killing me as to why this is happening.

When I go into the Network and Sharing Center and try to turn on any of the
'Sharing and Discovery' options (starting with 'Network Discovery'), I always
get the following message: "The Specified Service does not exist as an
installed service".

I am running a full version of Vista Ultimate. Not an RC or Beta. It was
an upgrade.

The reason why this is annoying me so much is that I have an Xbox 360
connected to my network and while the Media Center Extender functionality is
working, the 360 can no longer detect my Vista desktop to access the shared
folders while in the 360 dashboard. This always worked when I had XP running.

Any ideas why I can't turn on any of the Sharing and Discovery features?