I'm a new user and i was downloading music videos to use in a presentation for school. I was downloading .mpg 's, but they will not import to imovie, so I tried downloading a .wmv....that won't open in imovie either, and now none of my .mpg 's will open at all!

so I guess my questions are...
1) what video file types will open in imovie?
2) why will my .mpg's to start playing again?