On some sites (thatvideosite.com, compufused.com, etc), video clip sites, they wont let me play the videos. It says missing plugin, or unknown plugin and it has a little green puzzle piece symbol. I clicked it and it brought me to this website full of plugins and i installed them all (flash, quicktime, etc.) but it still wont let me play them. Some sites let me play their videos and some dont. Its a brand new computer, it was a display model so everything was setup and good to go. I have windows media player 10, realpalyer and quicktime. Is there a plugin i am missing????

Adobe Shockwave Player? http://www.adobe.com/products/shockwaveplayer/

Adobe Flash Player? http://www.macromedia.com/software/flash/about/

Go HERE to test if you have both of them and which versions. If the animations play you have them or it if its one.

These are frequently requred on top of the ones you listed. Make sure you have them.

...they wont let me play the videos.

When I clicked on the video's it brought up a screen to play in Windows Media Player and it played perfectly.

Check your File Associations as I used to visit that site and the video content is .wmv