no root

I purchased a samsung dart from target, it is a prepay phone card setup. I have read and tryed a couple of root programs and nothing happens. its almost like t moble has some how locked so i can not root it. any ideas?????

 

update to my post..I rooted the dart, yyaaaa. after more research i found i needed to down load the samsung driver pack called Kies. once i did that and ran the oneclick root program everything went perfect.