Dishwasher makes humming noise and will not cycle

When I turn the knob to on my diswaher makes a humming noise but it will not fill with water and the heating element does not get hot.

Hi. I have had the humming noise with our Zanussi and it was caused by the water inlet having crap on the inlet side of the water supply this stopped the machine from being able to move the cycle on and all we got was a humming noise if the cycle dosen't start this could mean that the element does not get hot because the cycle can't move on to the heating position. Hope this helps if i'm wrong I'm sorry. Bill.

has the machine overfilled at any point?
some machines have a float switch in the base, and if the machine over fills, maybe due to it not emptying properly the float switch is activated, its basically a fail safe to protect the motat ect from shorting out in the water, and to stop you getitng electrocuted.