Why have the music videos i saved on you-tube suddenly become unavaliable?

Answer 1

Google is making a serious effort to remove illegally posted material.

Music videos are still around, but it's going to get increasingly difficult to get hold of such material.

Answer 2

If you are talking about copies of music videos (Such ones that came from say, MTV?) they are usually removed by the original copyright holders of the media you saved to youtube. It is because they can reason that it is copyright infringement. (ie, making a copy of something that they didn't allow to.)