is your usb drive formatted for FAT32? over 4gb it's almost likely formatted for ntfs which it won't recognize.
plus it depends on the video codec too. some won't recognize xvid and some won't recognize divx.
your best bet would be to take these videos, find yourself a converter program like ConvertXToDVD and drag/drop them into there and burn them to a blank disc.
torrent the program. it's up on pirate bay and it's a great program.