All of a sudden, all of my recorded video collection won't play. Can you tell me why and how to fix it?

Are these videos you made or videos you downloaded? What type of files? What player are you using? Do you get an error message? Have you tried rebooting your computer?

Yah, they were files I downloaded from the web and other users. Everything was fine, then one day, nothing. It usually opens with Windows Media Player, but I can't open any video files using any player at all. I just click on them and nothing happens. I rebooted several times.

check you file associations in media player. what version are you running?