This is a super newbie guess, but do you think your 2-way switch (I am assuming this is what you have) may have gone bad on the side that controls "shade up"? Do you hear sound when you press up, like the shade motor is trying to do something? If so, I would guess it is a motor problem.
Conversely, the "up" wire connection to the switch may have fallen or broken off over time, which would explain why it works in one direction but not the other. I'm not sure exactly how the switches and/or panel comes off in your rig, but that is where I would check first if you don't hear anything when trying to roll the shade up.