DavidR
6
Where did you get the installation file for 5.1.1489 as its virus definitions will be massively out of date.
So as I mentioned the avast update process would see that it is massively out of date and probably be trying to download the full database rather than try to would out what VPS updates have been missed (hundreds/thousands) it would download the full database. That may make it appear to be doing nothing as the full database download is around 93MB.
This is why I suggested you download from a library or a friend on broadband.
Manual update of VPS - avast! Virus Definitions Update - Manual Download VPS Update (virus definitions, vpsupd.exe, approx 93.4 MB). - Save the file to your hard disk, locate where you saved it and double click it and that should carry out the virus definitions update.