The Time Turner can only be used with great caution. If used incorrectly, it can cause the entire future to change drastically, and maybe even cause death, or someone's existence to be undone.
Harry Potter and Hermoine used it under Dumbledore's guidance, and only went back a short distance in time. Hermoine only had it so she could take multiple classes, and it was returned to the Ministry of Magic after.
Actually, if I remember correctly, it said somewhere that the Ministry had destroyed all of them. (Yeah, this is what people get when they WATCH the movies instead of reading the books; you're not gonna know anything.)