USB drive won't show files in Windows, but fine in Mac OS

I have to give a bunch of video files (.mp4 and .mov only) to a client for work. At first, the flash drive was formatted as Mac-Os (journaled). It wouldn't show any of the files I had copied to it, just an empty drive. So then I re-formatted the drive as MS-DOS (FAT) so it would be compatible with both mac and pc. Yet when I went to try it again on the pc, it still just showed an empty usb drive. I don't understand why it won't show on a pc but will show on multiple macs.