Many users have been complaining of issues after the GDR2 update to their HTC 8X, up to and including the device actually being bricked.
WinPhoneViet ran into the same issue and contacted HTC, who were kind enough to send them an original ROM for the HTC 8X, in both Asian and European versions.
They have now made the ROMs available with full instructions for their flashing, which seems to involve a lot of software from the Windows Mobile era.
Find the download and full instructions from WinPhoneViet here.