New Philips Sonicare toothbrush doesn't 'brush'?

I've just bought a brand new Philips sonicare HX6731/02 electric toothbrush but, after charging it for the required 24 hours, all it does is basically make a noise - it doesn't make any type of 'brush' movement. If I wanted to just have something purring, I would have bought a cat!
Do you think I haven't put the toothbrush together properly? I'd prefer to ask before going to the trouble of re-packing, taking to the postoffice and going through the hassle of communicating with Amazon. Thank you in advance for any advice.