For security reasons I would sort this ASAP
Why not uninstall and try a new copy from magazine disk or download and then see if that will update to latest definitions?
Ensure Zone Alarm programme permissions is set to allow AVG to access net
There have been a number of threads here about the difficulty of updating AVG free version
If you still can't get it to work I would ditch it and try Avast instead. You sure can't continue to run without updated protection