You may have already come across these in your own searching, but thought these threads could be useful:
http://www.doityourself.com/forum/ga...t-furnace.html
http://www.doityourself.com/forum/ga...-not-heat.html
On occasion, I've had electronics (not a furnace) "freeze up" after a lightning storm, especially when the power flashes it seems.
I've had some luck by tripping the breaker on a given circuit and for whatever reason, the device will start working again after I reset the breaker.
But you indicated you've already cut power to the furnace, I assume by tripping the breaker.
Could be grounds and I suppose you could try reversing the low voltage leads as suggested in the 1st link. But that was a new install. Don't know electrical enough to know if polarity can magically reverse without actually swapping wires around (including I guess the main wiring to the house?). Your situation sounds most like the guy in the 2nd link. He had a bad board.
Hope you figure it out!
BTW, I love the fuse into the ether. I've been there before.