Here are a few threads you can read that might be related to your problem.

Read reply #25
http://forum.avast.com/index.php?topic=120561.msg924469#msg924469

http://forum.avast.com/index.php?topic=115192.msg937190#msg937190

Reply 25 refers you to a video, that has no sound and is not very clear.

ncpa.cpl is being typed in the search box. This will bring up your Network Driver. You will highlight it, and right click on it. This will show you a list of drivers installed that are probably not shown in Device manager.