1st: Check the trap at the bottom of the dishwasher. You may have to remove a plastic cover that means taking out screws. There's a chance a piece of silverware or possibly even a piece of food is stuck in there especially if you don't have a chopper in the bottom. (My dishwasher has a chopper but even w/the chopper, it can only chop up to a specific size). Clear out any debris, utensils, and/or other things that are beneath this cover.
2nd: If there is nothing under the cover, you may want to try a cleaner made specifically for dishwashers.I can't recall if it's Cascade or Jet Dry that puts it out but it's in a bottle that you turn upside down in the utensil basket and then run the dishwasher without dishes. It's to clean the dishwasher and remove any stains and debris. It leaves the dishwasher smelling nice too. I've always found it with the dishwasher detergent and Jet Dry products.
3rd: If #1 or #2 doesn't work, you may have a clog and for that, you will need a plumber because any of the de-clogging liquids can damage a dishwasher. Contact your local plumber if it appears as if you have a stopped up drain.
In the many years I have had a dishwasher, and it's been many many years as I don't care for nor do I wash dishes by hand if I can help it... it generally turns out to be something stuck in the bottom like a piece of silverware or something or even the dishwasher needing cleaning with the cleaning product made especially for the dishwasher. Usually options #1 or #2 work for me. I hope it does for you but if it doesn't, don't be beyond calling a plumber to fix the problem without making it worse.
Best of luck...