Default [Q] Rooted a SGH-i317 with N7100 components and now it does't connect to AT&T -HELP-

My first time rooting my phone, I've had a rooted phone before, but my friend did it for me so I never actually had to do anything. After a year of thinking about it and a purchase of a Galaxy Note II, I thought "hell, why not." I'm quickly realizing my mistakes. I have rooted it completely with the International N7100 version. How do I get it back connecting to AT&T (My phone does not attempt at connecting to the AT&T radio anymore.) I am in dire need of a solution as I do not have the fund to purchase a new phone. The SIM card is fine, I just need a remedy to get my phone back on AT&T track before my money goes right down the drain and maybe worse. Please respond, I will be in your favor.