It Doesn't Turn On
A dishwasher refusing to turn on at all can indicate a serious problem. Before calling a repairman, there are are a couple of things you should check.
First, make sure that the machine is receiving power. Check that the power cord is plugged in and that you have not tripped a circuit breaker or blown a fuse.
Make sure the cord is fully intact; look for burns or tears. Next, make sure the door latch is working properly.
Often machines will not turn on if the door is not properly closed. Make sure that the door is not obstructed or damaged.
If these measures fail, you may need to call a serviceman to inspect the motor and the internal wiring.
It Won't Drain/It Leaks
Some dishwashers run fine, but will have problems with the water used during the cleaning, either refusing to drain it or leaking it out onto the floor. If the dishwasher refuses to drain, this may be a sign that the drain is clogged.
Open the dishwasher and check that the drain is not obstructed. If the machine leaks, try to locate the source of the leak.
If it comes out the front of the machine, it may mean there is a problem with the seal; if it comes out the bottom, it may indicate a leak in a hose or a pump. If it leaks bubbles, you may simply be using a detergent that is too sudsy.
It Doesn't Clean Well
Some machines simply stop cleaning well, leaving pieces of food or spots on the dishes. If the dishes have food on them, this may be a sign of a broken scrubbing arm or motor, or it may simply be that your water pressure is too low.
Check the pressure that you receive on other faucets. If the dishes come out of the wash with spots or a thin film, this may be caused by the presence of hard water minerals in your tap water, too much detergent or a water temperature that is too hot.
Adjust your hot water heater so the water is as close to 140 degrees F as possible.