[Q] At&t Htc One X won't pick up signal. topic

I bought this Htc one x on ebay.com and it won't pick up signal. The issue is really rare to me since the phone does read the sim card. It won't pick up at&t or t-mobile signal in my area. Don't know why because both sim cards work, I tried them on my atrix hd and it does pick up signal. How can I fix this issue?