NO GREEN LIGHT ON MEDIA SHARING

I HAVE A HP MEDIA CENTER COMPUTER THAT I UPGRADED TO VISTA AND I AM TRING TO
ENABLE MEDIA SHARING FOR MY HOME NETWORK. I HAVE CHANGED THE NETOWRK TO
PRIVATE AND I HAVE MADE SURE THAT THE NETWORK NAME MATCHES MY HOME NETWORK. I
WENT INTO WINDOWS MEDIA PLAYER 11 AND ENABLED MEDIA SHARING THERE. WHEN I GO
TO THE NETWORK AND SHARING FOLDER AND TRY TO TURN ON THE BOTTOM BUTTON,
"MEDIA SHARING", IT ALWAYS WILL READ OFF, AND NO MATTER WHAT I HAVE TRIED IT
WILL NEVER READ "ON" WITH A GREEN LIGHT. ANYONE HAVE ANY IDEAS ON THIS MATTER?