Whirlpool dishwasher

The very first thing to check is the float inside the tub. Most of them look like a mushroom in one of the front corners. Raise it up and drop it back down. It should move easily and you should hear a slight click as it sets back down. It is common for the float to get knocked out of place by something sticking through the rack when you pull the rack out.
Post back and let me know if this helps or not and we will check other things if needed.