Unable to factory reset my HTC Desire S

I have a HTC Desire S. I have firmware updates but when i try to update the same. I rebooted in the updating process and the phone hangs there for hour (i waited for 4 hrs once). I tried to factory reset the mobile, still facing the same issue. Note: The phone is rooted. Do I need to visit HTC Service center or is there anything that I can do?