Try to download again ..and see if they appear displayed when you have to select what to download..If you did not selected all of them than this may be an issue ..and it downloaded only the first one auto-selected..
Also check to have space where you download them ..
If the videos are not only on the internal memory ...check if teh card appears displayed when you try to download..if you use the software that came with the camera ..and it has a card ..the card may not be seen when you download,,,and it only gets the stuff on the internal memory ..(i suggest to use teh card directly in the card reader )
For mac users..there is the issue on seeing the videos if they are in a certain format ..so ..check you camera settings to see what kinda format are the videos in it ..and than download and install the codec for them (for example mpeg 2 vidoe codec..its needed for most of them )