Why are some songs not playing in my Music playlist?

I have over 2000 songs on my MacBook pro, and now I'm trying to make a new playlist. After creating a list with only 8 songs, I realized that only 2 of 8 would play. I went back to my song list and discovered that a lot of songs would not play when I selected a song but would play a song further down the list. It's as though the songs previous to the song that's playing, are no longer there but yet they're still listed. NO exclamation points there.

[Re-Titled by Moderator]