If you do you probably have to step back on page 1 and reload the file default.conf (bottom of the first post - If you want to revert back to the default nokia boot video(Hands-v32-h264.avi) copy this default.conf)

also if you would like to check if the video is there do this on terminal

sudo
cd /usr/share/hildon-welcome/media
ls

after typing ls you should see the files inside that folder and you should have:

Hands-v32-h264.avi
matrix.avi

if is correct replacing that file should be enough, if you have the video "hands" twice you have to remove one.