AVI file, sound no picture on Mac

I’ve downloaded a few .AVI movies to my ppc IMac with
Mac Os 10.4.9, they played fine using
Quicktime 7.1.6, today I tried to play some again and have
only sound, no
picture. this doesn’t seem to affect all the .AVI movies,
just a few.
I also opened the .AVI files in other players, same, have
sound no picture.
With no players I asked to see info on files, the small
preview screen was also sound no picture.
Is there a app to run to check on file corruption on my
mac ? Or could it be some other problem?