Smeg DI 409CA Dishwasher - Doesn't wash properly,...

Question

I have just bought a brand new Smeg dishwasher (model number above). It all seems to be connected ok, but on selecting any cycle the dishwasher will either go all night with the result being dirty dishes and the tablet still not disolved (it is in the door dispenser and is completely untouched). Or it will run the cycle for 2-3 hours and on completion the results are no different to the overnight cycle. If you repeat this operation too many times water builds in the bottom of the dihwasher. Any help would be appreciated - I don't want to call the service centre if it is something silly I have caused.
Thanks
Tracey