your problem is window update, why blame it in avast??? :'(
avast do nothing in window update,
in my experience of using window7 avast need also the windows update so that it will be adopted by the OS
and i do not see any reason that avast will block your update
just observe the video you play maybe its broken and WMP won't play it
try play in VLC even broken video it will play but until in the readable amount only
bong2x