When the 4 colour logo starts to build during initial boot press and hold the power button for about 6 seconds to ensure the computer goes off instead of standby. Unfortunately the timing can be a bit critical, sometimes you have to wait until the animation completes so can be a bit of a pain to get right.
Do this 3 times and at the 4th attempt the logo should have Please Wait under it and this time let it boot and it should get to recovery mode. Select the Reset option and that will return it back to factory settings and allow you to attempt setup again.