I just updated my new license key, rebooted the system, and my Windows XP is saying that I don’t have any virus protection. Please help to activate it again.
Thank you!
Hi, alexpustelnik.
I think it’s a good idea if you’ll take a look to Windows Security Alert for information and for more links about your question 
What is the exact error text from Windows Security Center (WSC) ?
Is the avast icon in the system tray ?
What avast processes are running in task manager, they begin with ash and asw ?
Which version are you trying to register (Home or Pro)?
Will this thread help? http://forum.avast.com/index.php?topic=23457.msg193534#msg193534