Climb up on a ladder, take a look at the very top of the door, you will see a small steel "stop" that has been worn so that it no longer holds the door open. Check to see if your door was manufactured by "PTL Engineering, if so you may be able to get a replacement as they are still in business;
Welcome to the Official Site of PTL Engineering
I just found out that is why my door will not stay open.
RUNDLC