Hi shasul,
Was the phone ever rooted, and did you change anything before this problem started?
If the RUU ran completely then the phone should have had a factory reset (which solves most boot problems) and a new ROM flashed (which solves many others), so apart from finding whether there is a better RUU for your device and trying that - for which someone who knows the Z could give better advice than me - it's not obvious what else to suggest. Can you at least confirm that the hboot and radio are what you expect for the RUU that you ran (gives us some indication of success)?