wow, a lot of possibilities here. . .
I think I'd make sure its at 70 degrees or so, and wait for awhile. It may be slowly going. If it stopped bubbling, are you sure you still have a good air seal?? (I.e., slowly going, but with a small airleak, you don't see the bubbles)
Other thing, was this a first generation yeast? I've had 2nd and 3rd generations stop, then start up again. (Those damned yeasties can be unpredictable).
leastways, I think I'd first RDWHAHB.