Recently I bought an HTC One X from AT&T to replace my iPhone. When I got it, I was prompted to update to the new update released by HTC on August 8th, 2012. Unfortunately after the update and after the reboot, I was left with an inoperable phone! The screen was black and the only thing that could be done was to hold down the power button to reset the phone. I tried a factory reset by going into the boot loader (HBoot), but no luck!
After reading some posts suggesting a factory reset from HBoot that did not help I tried reflashing the update using HTC’s RUU utility. The patch that includes the utility can be downloaded at http://dl3.htc.com/application/htc_one_x_RUU_2.20.502.7_att_us_08022012.exe (linked from the HTC One X support page).
Luckily, reflashing fixed my issue! Hopefully this helps someone else with the same issue not spend an hour on the phone with AT&T.