Jeri,
Go down to the Home Depot or Loewe's or whatever you have nearby and get either a 3" or 4" FERNCO coupling. If the pipe is strapped down, undo it temporarily so you can manipulate it somewhat. Ferncos are rubber pvc couplings sized to fit snugly and come with stainless steel band clamps. Check the side of the PVC pipe and you will probably see what size it is as they print it on there in a long stream of specs etc. Get some good rubber or latex gloves to use as well. Plumbers have to get in there and do this all the time and dysentary should not be a major concern unless you are a nail biter. ;~)
Ask an old guy wandering the aisles of your local hardware/lumber supply for more details when you get there. I think you can fix this one pretty easy, but something weighed yore pipe down to make it come loose so mebbe there's a blockage further down the line. If it's roots in the pipe blocking flow outside the house then you need a rooter guy.

Yerz,
Tweed