When i try using either Quicktime, RealPlayer or Windows Media Player i cannot see the video. All i hear is audio. Is there something that i accidentally disabled in windows or anywhere else?

Are these video files, DVD's or what?

videos from internet sites

Depending on the format they are in you may noit have the right video codec's installed. download this free app it should help you solve your problem.

http://www.kcsoftwares.com/index.php?vtb