Copyright and Youtube's Principal's Office

Ok, one more post on this my blog's inaugural day. I love music, the stranger the better. All of my videos have background music that is funny or inspirational or whatever. But here's the problem, some of the music I picked was copyrighted.
Have you ever tried to post a video on youtube only to have it regected because of copyright? I've encountered that twice. Then I got a message from youtube letting me know I shouldn't do that again. The message further informed me that I would be suspended or expelled from the virtual world.
I get that the guys who wrote the song make money when the song is played and paid for. But here's my thought, if my video is good (and that is a big if) I think it would make people go out and buy the song or the album. The other problem is some songs are copyrighted and some aren't. The website that I get the music from claims none of the songs are. Little did I know I would need a law school degree to make videos.
One of my two videos that had copyright issues will never be seen. The second video, "In Honor of the 44th President of the United States" was allowed to be posted. But if you look below the video, there is a link the song owner put on my video for people to buy the song. Fair enough.
So, please buy that song after seeing that video. I don't want to go back to the Principal's Office of youtube again.