Vista - Can't enable media sharing.

I am unable to turn on media sharing on my desktop.
My network is private and I'm able to see the desktop from the laptop and access shared folders.
I am able to enable media sharing on the laptop (running Vista Home Premium) and I have the "green" media sharing dot.
I have upgraded my desktop from XP to Vista Home Premium 32bit (hoping this would fix the issue), but it hasn't.
The "green" dot in the network and sharing center will not turn "green".
As a result, my Xbox does not recoginize the desktop, but sees the laptop.
I am able to access media with the xbox via Windows Media Center (but what a pain!).
The problem may lie in WMP-11, which I failed to uninstall prior to the upgrade. Now, I can't uninstall WMP because Vista recognizes that it's part of the OS. And, I can't install the upgrade for WMP-11 for Vista because I get an error saying it's not compatible with my system (it must identify it as an XP version). So, evidently I have an XP version of WMP-11 still installed and don't know what to do about it. There is no downloadable version of WMP-11 for Vista that I can find. Please help!