Guardians

For Nick Sorvas, seventeen, and an orphan of the stars, Earth is but a distant memory. Carson's Syndrome, a neurological disease caused by an unknown virus, has killed over eighty percent of the world's population. Humanity's only chance for survival is on another world. Nick, his girlfriend, Julie Adams, and five other survivors, including her father, Teller Adams, the captain of a starship, leave Earth in search of another home.
They crash-land on another world very much like ours-but not. They are the only inhabitants, and so they attempt to forge a new life together. Over time, they find out that their new world is called Xibreen, and that the former inhabitants are nowhere to be found. They have, however, left a considerable database of knowledge in a series of machines. Planetary history, though, will have to wait, as Nick, Julie, and the others have to contend with three members of their crew mutinying, as well as a vicious invader known as the Vorde. With few weapons, little training in warfare, and almost no hope, the small band of settlers decides to fight back any way they can.
It's only when Nick connects with one of the machines left behind that he finds out who the former inhabitants of Xibreen were, and what their real purpose was for leaving.