When we switch the dishwasher on it trips the electricity. It's worked fine for 2 years but now won't work at all and just trips the electricity.

Your dishwasher has a serious electrical safety fault which is causing the protective breaker to trip (although it may have a simple and cheap cause). With all due respect, your question clearly demonstrates that you lack the knowledge and skills to carry out a diagnosis and a safe repair (especially vital for anything which uses water and electricity). Before doing anything else, fully disconnect your machine from the main electricity supply by either unplugging it or for a machine connected to a flex outlet by turning off the wall switch and then removing the fuse.

Sorry, but in this instance you only have two choices: get a qualified dishwasher repair engineer in or replace the machine. Anything else could be lethal.