erm send it back- if you can boot for abit there is a temp soloution for stopping your unit rebooting tho- but it has a downside , it will drain your battery faster

if i was you-(well actually i am u , this is what i am doing)- call nokia say you are gonna send back for a replacement- but flash it, do the fix and see how you get on- if you still wanna send it back there are aware you are going to.(i didnt flash my unit tho)