Some days ago I tried avira, but I didn’t like it, so I decided to reinstall Avast. Now I have a problem with network shield: it always counts 0. I have already tried to disinstall and reinstall avast many times (I also used avast disinstall utility in safe mode and regseeker to clean the registry) but nothing. Can you help me please? 
Strange, I can see that mine NS is scanning webpages.
Was Avira fully uninstalled?
What OS are you using? Firewall? Any other security application?
Thanks for your prompt reply. Yes I use comodo firewall, but the strange thing is that before I installed avira, avast network shield ran perfectly and since then I haven’t changed anything in Comodo setup.
Sorry, I forgot… I have windows vista and Avira was fully uninstalled…
Try the AntiVir registry cleaner as described here:
Also - Avira AntiVir Uninstall Package & RegistryCleaner (choose appropriate version): http://www.avira.com/en/support/support_downloads.html.
Can you try stopping network shield and starting again? Normally it shoudl start automatically, if this helps we know it is a problem with startup.
Well, first I used avira registry cleaner as DavidR suggested, then I have also uninstalled and reinstalled only the network shield module and now it seems ok.
Don’t know what was happened: for what I know, avira free doesn’t have a network module which can interfere with avast.
However thanks again for your help! This is a fantastic forum! 
You’re welcome, glad that it is working OK now.