Only 2 clips (the ones i was editing motion graphics on) are playing back, all othe clips gone black

So I was following this tutorial for a transition (starts at 7.51). I completed it, but when I was going to run through the entire project I noticed everything else has gone black and the song doesn't play. APART from the two clips I edited (technically 4 as two of them are duplicated as instructed in the tutorial) although the song doesn't play here either only the video's audio. Please Help! The newest AE version is being used and I didn't add CC scale wipe to the duplicated clips (as shown in the tutorial).