There's little about this group online other than their only hit(?), "Happy" from back in 2001.
Discogs (no idea of the list of members there is accurate)
"Happy" is a song by German group Square Heads. The song was released in 2001 on ZYX Records. The song is known for playing a key role in the development of the commercial trance sound, and has since been considered an electronic/trance music classic. (from video below, "Square Heads - Happy (Original Promo Video 2001) [Remastered]")