Help? Youtube Videos De-Ranked and De-Indexed

Hey, warriors, I have a fairly big problem here and I would really appreciate some help.

I uploaded about 50 videos to Dailymotion to rank for some low-competition keywords in a niche I'm trying to dominate right now. They all ranked somewhere on the first page for their keyword, but the thumbnail wasn't there for most of them. Only about 5 had the thumbnail even after a week.

So I took them all down from Dailymotion and uploaded them to Youtube, targeting the same keywords as before. Once again, they all ranked on the first page and this time the thumbnail was there instantly, so I thought I was in the clear.

I just looked at all the keywords, and now only 1 of the 50 videos I uploaded to youtube are on the first page. The other 49 aren't even indexed. The weird thing is, the dailymotion results are still up there, still without the thumbnail, even though I deleted all of them.

How can I get my youtube videos to rank on the first page again? Do I have to reupload them, but change them slightly? Maybe target different keywords now? I'm thinking the previous dailymotion results might be triggering some duplicate content penalty even though they were taken down.

I read something once about there being a duplicate content penalty if two videos have the same audio track, which all my videos do because I made them on Animoto and used the same song for all of them, so not sure if that's the problem.

I really need to fix this problem before I can move forward. Thanks in advance for any help you guys can throw my way.