Xbox 360 and Windows - "PC Not Listed"

[Chernobyl]

I have connected my Xbox 360 by an ethernet cable straight in to my computer and have connected to Xbox live through ICS and am also connected to Windows Media Center.
But no matter what I do I can't connect to Windows Media Player and set up media sharing.
On my computer, it knows my Xbox 360 and I have allowed media sharring to it but when running the PC connection test it comes up with the "PC Not Listed".
HELP ME PLEASE!!!

I'm running Windows Vista Ultimate and thought this is a network problem because it connects to my network but can't find my computer even though the only things on the network is my computer, my Xbox 360 and my wireless dial-up internet.

[Chernobyl]

Fixed it if anyone one else has this problem.

It was the firewall in norton internet security.

I didn't find a way around it but disabled it completly and am relying on the firewall in windows vista