Video problem

I'm using Firefox, Windows Media Player 11, and have a DI-604 Router...

It seems that recently I haven't been able to view videos on my desktop.

When I'm on the web, and see a video which I'd like to view, I click on it, and the browser screen will turn white, also any links to videos don't work...but If I'm on a website like YouTube, the videos are fine.

On very few occasions, Firefox opens a little window and asks if I want to open the file with WMP...but I thought that WMP would be my default automatically. It seems this problem started after I upgraded to WMP 11...

I'm okay with my PC, but get frustrated trying to set things up properly...

Any help with this, or a link to read would be greatly appreciated...

Thanks