Check your dishwasher is connected to a power supply and that its circuit breaker hasn't tripped. You should also make sure your machine is turned on and is not already in the middle of a cycle. Check your washer's user guide for information on how to reset your machine if it is.
Ensure the seal around your dishwasher's door is free from dirt and debris and that its door latch shuts properly. The door of your machine needs to be able to close securely before you begin a cycle.
Press down on the overfill protection float, if your machine has one, to make sure it's working.
Inspect the water inlet pipes at the back of your washer to make sure they are connected properly and are delivering water to your machine.
Remove the shelf at the bottom of your washer and inspect the filter to make sure it's not blocked.
Check your washer's drainage pipe and your clean water sewage outlet for obstructions.
Rinse all items you put in your machine under a tap and be careful not to overload your washer. If the spray arms are blocked, your dishes will not get clean.