flashing light goes to rinse mode?

Hi my dishwasher problem seems similiar to some of those listed - switch on the normal 40 degree wash cycle - within a few seconds it startes to beep - the light on the far rights flashes and the light has moved from the 40 degree setting to the prerinse symbol.
Have taken bottom plate off - no water in the bottom - have tried pressing black switch on right 4 times - not worked. Any help will be so gratefully received as I am driving husband and kids mad with constant moaning about how long I am stuck at sink washing up!!