Help Realplayer doesn't work now. Thanks a million.

It works for one movie; it doesn't work for the other movies on my hard drive. But these movies all worked when I downloaded. Then I re-downloaded Realplayer, it still doesn't work for these movies. I saved all these movies for my My old folks. But now the Realplayer can not play. I'm so fruatrated.Anyone can help me with this problem? Thank you very very much.