Hi
Try opening the Network and Sharing Center, (right click on you network icon on the task bar, lower right) and select Change adapter settings.
Select your connection and click on Disable this connection.
Wait for 30 seconds and click on Enable this connection.
See if that reestablishes it.
Check you computer to see if you have Bonjour Services installed.
It is installed by Itunes and several other programs.
If you have it uninstall it.
Hope this helps, if it doesn't come back and some one will pick it up from there.
Mike