First of all, if the machine is running the door is supposed to be locked, so when your brother opened it he probably did not do anything (yeah, I am on his side on this one, but it is still probably a good idea to keep him away from the machine). It was probably not locked to begin with. Does the "door locked" light come on?
I would disconnect the machine for about 10 minutes and see if this does not reset things.
If not, you are probably looking at an expensive repair to replace the door lock assembly, or using it as is and remembering not to open it while it is running and not to let your brother do so either.