Videos on CD disappear

I have a series of videos, burned to a CD in various formats, AVI, MPG etc.
They were originally burned to the CD using XP. Two days ago, on my current
laptop running Vista, I was able to see the files on the CD and play them.
Today I go back to view them on the CD again and they are gone. I believe
they are there, but do not show. I have checked the folder options, searched
with Explorer and even tried to start them from Window Media Player using the
most recently played files choice, but it says they can not be found. I’m
running AVG, if that is relevant. There were too many files to have
inadvertently deleted them all.