Okay, this is going to be tough. It's driving me crazy because I have this song stuck in my head, but I don't know who it's by or the name of the song. The thing is, there's no lyrics to the song. It's mostly piano, with a happier sound, and there are some vocals, just "oo"s and "ah"s. I think I heard it sometime between the years 2003 and 2005, if that helps.

It is more than likely a song by Enya