A common reason a Frigidaire dishwasher door might not close is if the racks aren't pushed in all the way. Racks may get off track and not slide all the way back or slide smoothly back and forth. To fix the problem, lift up on the rack and line the wheels back onto the track. You should then be able to slide the rack all the way back and close the dishwasher's door.
If your rack slides back to a certain point and you still can't close your dishwasher door, something may be in the way of the rack. Pull the lower rack forward and look at the bottom of the dishwasher. A dish or piece of flatware may have fallen off the rack at some point. Remove the item and slide the rack back in until it stops. A similar problem arises when items hang over the front or back edges of the rack.
The doors of certain models of Frigidaire dishwashers must be pushed all the way shut to engage the locking mechanism. If your dishwasher door appears shut but you can't start a wash cycle, give the door a push to close it completely. You should feel and hear the door lock into place before the wash cycle kicks in.
Certain older models of Frigidaire dishwashers have a lever on the front that you move to one side to lock the door shut in order to start the wash cycle. If this lever is already set in the lock position, you won't be able to close the door completely. Move the lever to the opposite side and then shut your door. To start the cycle, push the lever back to the locked position and press the button that begins your wash cycle.