Sorry to hear you had problems. If you had come here before you switched to avg
we probably could have helped you with the computer slow down. We've done it before
and we'll do it again. If you so desire our assistance please uninstall avg using their removal
tool and reinstall avast.
Then provide more info...
OS?
Any other security software you have now or ever had? (firewall, anti-spyware, etc.)
If uninstalled how was it removed?
Which browser?