iMovie Preview Showing white screen

I was using iMovie 09 for the 1st time the other day and when I imported a video the thumbnails show fine in the timeline and the sound works but in the preview (both full screen and the small screen one) shows just a white screen and plays the sound. I then installed iMovie 11 and had the same problem still which suggests a codec issue. QuickTime works fine though and it is the most recent version. I've tried downloading Perian,xVid and divX codecs and it still wont work. Andy suggestions?

Ok sorted, I needed to download the codecs I mentioned then delete the boot playlist for iMovie (user/library/prefrences/com.apple.imovie)