While I can use AVG, Avira, the AV from google or other I don't limit myself to just one or the other. You might want to consider the alternatives.
But let's say you are stuck on AVG. You could try the CNET AVG Forum where they supply the link for the FULL DOWNLOAD that does not require an internet connection. That is, you go to some free wifi spot, grab the file and take it home to the machine that won't get to the AVG and install it there.
There are far too many reasons for your machine's failures. From OPTUS to an expired old antivirus to other. There's nothing in your post to start in any direction so I'll leave it at how I can get AVG onto a machine that can't get it on its own.
I have just bought a pre-paid stick from optus because we were connecting through wi-fi and it wouldnt let me install AVG, now that i have this prepaid it still says it cannot connect. (AVG that is) I browsed through questions on this site and found the question i needed to help me install AVG but when i click on the link to download the programme the page wont show as dont many other AVG links i click on. I have the error code 0xE001003D, i know there is nothig wrong with the link so why are my pages not loading. I dont have a problem with other web pages? My OS is XP.