AVI files work in-camera but not on computer?

I have a Nikon d90 and I took some videos on it. When I play the videos in-camera they work fine but when I try to upload them to my computer about 4 of them don't work, and instead of having the video thumbnail they show up as blank white squares. I've tried converting them to a different format and it didn't work. Any ideas on how to fix this?

Added (1). Jim, I've tried multiple programs and nothing is working. It's only a few of the files that aren't working though, most of them do.

We would need to know WHAT avi format they are in, but otherwise, your best option would be to download a codec pack

Also the program you're trying to play them with is probably the problem, it can't read these files.
I'd agree, a codec pack may help.