some avi's stop working in WMP

Can anyone advise why some avi's now fail to play in WMP?
They did before.
I have several codec packs installed, before this issue occurred.

 

That could be your problem. If you're gonna use a codec pack, try using only 1. Also, check the problem avi's with gspot codec info (should be with one of the codec packs, if not you can d/l it here: http://majorgeeks.com/GSpot_d4293.html)
Gspot will check which codec(s) it needs and whether or not its installed on your computer. Also, do they work in vlc? vlc uses it's own codecs (unless you tell it otherwise)
http://majorgeeks.com/VLC_media_player_d4674.html
this will help you figure out if the video works.

 

Thanks for your help, I've tried not to clog up my pc with extra software, and have always used WMP, and refrained from using VLC for years, and haven't yet needed it.
I know they work, as they have done, some recently, others further in the past.

Just used gspot to check one and, although it doesn't seem to provide a clear answer?!!?!?!, i.e. not a very easy program to use, a one place i think it says at stat: codec(s) installed............so whats up?