If you like AVG and want to continue using it, probably your best bet is to completely reinstall AVG.
The newest version is 8.5. You can download it here
Save the downloaded file to your desktop. Uninstall your old version using Control Panel --> Add/Remove Programs, then immediately after closing Control Panel, double-click the new AVG installation icon that has been installed on your desktop. Follow all of the instruction dialog boxes, with your last step being to check for updates to the AV definitions. You should be okay then. The whole process won't take you more than 15 minutes (most likely).