Just to say that after contacting microsoft about crashing issues with the sons xbox they came out trumps imo.
I contacted customer services by email, they replied suggesting I try the usual steps to resolve the issue but contact them again if it did not work.
They dealt with my follow on call efficiently, emailing me a label to send the xbox back by ups, about a fortnight later we had another xbox through, which seems to be working a treat

Well done microsoft on this one