How come video files won't play on my computer?

When I download videos from other sites or videos from the camera on my iphone, they download to the computer and the files themselves look like pieces of paper with a QuickTime logo on them. However, I can't watch the videos on QuickTime or on Windows Live Movie Maker because I get some errors. The error code on QuickTime is 8971, and I'm unable to play the video. What can I do?

Just download this video player:

http://www.videolan.org/vlc/

This is VLC media player. It can play any videos and any music and audio files.

It is very very useful player. Almost everyone uses it.

So, believe me, This media player can play any video in your computer.

Get some codec pack and install it on your machine,. L