Can't open downloaded files in Vista Ultimate

Hello,

About two months now, can not open downloads of any kind, be it files, updates,games, pictures, etc.
Didn't do anything different before this happened. Everything downloads with no problem, when I click to open the download nothing happens. Can not get any of my updates, with my window updates it states error 646. With my AVG Security updates, it just doesn't update at all.
I tried running the system in normal instead of safe mode.
I drfragmented my files, nothing happened.
I tried oopening updates individually, nothing.
Can anyone help?
I need my files
TThanks