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It sounds like your control lock has failed. To unlock the door, remove the 3 screws along the bottom of the lower front panel. The panel will then pull straight down and off. Once you remove this panel you can reach up behind the upper front panel and pull down on the small plastic pull tab attached to the bottom of the door lock assembly. This will manually unlock the door so you can open the door.
Then you can try to start another cycle and if you run into the same problem, replace the door latch.
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