Intense experience with Ouija board

This happened many years ago when my friends and I were still in high school and I will never forget it. One of my friends (I'll call him Ed) had just moved out of a house his parents were renting and it sat empty for several months. He knew a trick where he was able to still get into the house by lifting the rear sliding glass door out of the track and a bunch of us would hang out there from time to time without anyone knowing. One day 4 of us, Ed, Sam, Jim and myself decided to cut class and go hangout at the house. One of them brought an Ouija board and I was all determined to see if the thing really worked or not. I had tried them a few times in the past without very impressive results. We set up the board in the den where we usually hung out. It was a dark paneled room with a brick fireplace on one wall and a door that led down to the basement which was open at least 3/4 of the way. The Ouija board was the standard type made by Parker Brothers which you were able to find at any Toys R Us at the time and probably still can. I sat on one side and Sam on the other while Jim and Ed just hung out in the background nearby. Jim and Ed both thought what we were doing was silly. I was all serious hoping to find out if it was for real and Sam was acting a bit aloof. Sam started asking some questions that I don't remember specifically but the board spelled out a date or a year in response. Sam claimed it was Billy the Kid's birthday or something like that and I assumed he was just being a silly jack*ss and purposely moving the marker. Then I got serious and said "if anyone is here show us a sign". We took turns saying this over and over several times and nothing happened - the marker stayed still on the board. We kept saying it "If anyone is here, show us a sign." Ed and Jim were like "this is ridiculous." Then maybe the 9th or 10th time we said it, all of a sudden, the basement door that had been open the entire time slammed shut! No one was near it and no windows were open in the house. There was no air movement. It just slammed shut all by itself. We all froze and Ed walked over to the door and opened it. As soon as he let go of the door, it slammed shut again! At this point everyone was freaking out except for me (somehow I found this really interesting) and they started running out of the house - me running after them. Later, I asked Ed in all the years that he had lived at the house, did he often leave that door open and if so, did he ever see it close by itself like that. He said yes, it was often left open just like that but no he had never ever seen it close by itself!