yep mine does this, gets to starting up (no little red clock) then just resets, over and over again.
called the helpline, the lady actually got angry with me as she was convinced it was working fine???
tried to explain that i had 2 boxes and yes one was working fine but the new one wasn't - she wouldn't have any of it and accused me of not actually plugging the new box in!
after 20 minutes of me repeatedly telling her it wasn't working she told me i would have to have an engineer around - that was a week and a half ago - the engineer is due tomorrow (although i haven't had any confirmation that its booked) - i will let you know what the outcome is, my suspicion is a duff box.
Yes that's what I think the box is knackered and they have done the same sending me round a engineer on Friday this was reported 2 days ago they don't really care if u got to wait a week or so it should be next day service