.avi codec problems

ok, got 2 .avi files, one played perfectly with just ffdshow installed, the other had good video, but no sound. I installed Nimo Codec Pack, the .avi without sound is now fine, but the one which was fine in the first place is now all green & pixelated, no video or audio at all ! Is this a conflict between the 2 codec apps, and, any ideas how i get around it ?? Ta in advance.

Dene