I think it would be a good idea, like Talon suggested, to check your pH. Additionally it may be a good idea to check your total acidity. If it is too high, you'll want to add some calcium or potassium carbonate to lower the pH/TA into a viable range for your yeast.
Also, I think once you have tested the pH and TA you might want to make a really aggressive starter, rack and re-pitch. The reason I say to rack is because your current vessel may be fouled. I don't mean "fouled" as in taste, off flavors or anything in the usual sense. For me, it's about getting the must into a new, fresh, sanitzied container, re-pitching and topping it off. I'm just wary of re-pitching in the same primary I have used already because of the dead yeasts, etc. already there.
Also, this may be really funny but. What kind of orange did you use, and did you scrub it good and hard on the outside to remove the pesticides, sealer? I am paranoid as a meadmaker and when I get fruit like an orange with a thick skin, I take a 3M scouring pad to the skin with a weak peppermint soap solution to get the wax, sealer, pesticides and crud off the outside. You also "open" up the skin and make it a little more permeable for flavor extraction when you do so.
Hope that helps,
Oskaar