IMOVIE WONT PLAY CLIPS! 0 IN CORNER!

Ok, so this is the 3rd post ive made on the forums and it seems like no one can help me so im going to try one more time before i chuck this macbook out the window. Ive been editing reviews for games and movies for a while now and this is the first time this problem has ever happened. All my clips the the prject im reviewing now have been ripped and converted form the same source. The clips i added this morning work, but now its doing this thing yet again where whatever clip i convert to my .mp4 and import doesnt play! The audio is there and plays like normal but the actual scene it self is just a still image for how ever long the clip is. I dont understand whats happening and like i said i cant find anyone who can help me. Im begging here, please someone help me find a solution!

in the screen cap below you see a clip i imported that plays fine (the framemwith John Hammond) and next to it is the frame that will now not play at all, it has a little yellow 0 in the corner (i assume saying it has no fvrames per second) and only plays the audio of the clip.