Assuming the hinges are still attached to the door and have simply come out of thier slots on the main part of the oven.
Look at the top of the hinges they have a piece of metal on a hinge - a bit like a zippo lighter lid. Open these so they are not closed over the main metal of the hinge. Pop the hinges back into the slots on the oven - hold door half open. Close the metal hinges down again - it should close now.
Bill
September 2008