Video files severely altered after I just renamed them !!! HELP !!!!

Archos Tablet, Android

I can not play them normally (have to install another player app, and the video has lower quality), can not renamed them anymore, have trouble sharing them (have to use other player, or converter).
When I want to copy them in another folder, it’s only 1 0b file (instead of the 2 video files). When I look for them in ‘gallery’ they’re gone ! Same as in the camera app !! WTF????!!!!!!!!!!!!

What can I do to get them back at their proper quality ? I used XPlayer but even with that one I have some trouble.