Hard Drive shows some files, not all

I am a salesman in a tech department of an office supply store, and I had a customer issue stump me today. She had an external drive with lots of files on it she wanted to access. I took the drive, plugged it into a Windows 7 machine (HP quad), and all of the files appeared, no problem.

But, then I plugged the seagate drive into her new Toshiba laptop (also Win 7), and only some of the files appeared. Missing were all photo files, and many other types. I could not figure out why some were missing and some showing.

I took the drive to a third computer with Win 7, an MSI all-in-one, and behold: files were missing. Now it seemed almost arbitrary. Could it be a matter of some Windows updates not yet installed? Why would the exact same drive work differently on three different computers in regard which files were seen and accessible? None were "hidden" files.

What on earth can cause this?

My first shot would be to reset default file associations on her laptop.
https://www.sevenforums.com/tutorials...s-restore.html

I've reset file associations by right clicking on icons, but I've never had icons become invisible altogether when file associations are altered. That is so...weird.

Some installed media programs can cause issues with looking at media files specifically.

I've seen where altered file associations can prevent a media file from launching, but make it invisible? I know, I'm being redundant.

I don't think it would be the disk itself as the files are either there or not and shouldn't be visible on any computer if they are not actually there....A second question - was this a simple usb external or did it have its own power adapter included?

Right, the Seagate USB external drive works, and I can access its files on some computers but not others. The drive is USB powered, not requiring an AC adapter. I had the "invisible files" issue on both a laptop and a desktop.