I can offer you a possible fix that seems to fix mine (I have to do it every year):
Reattach the head and make sure it is securely attached and latched.
Fill the cauldron to the line with water and plug it into the witch.
Turn her ON, but leave unplugged. While holding the purple "push to animate" button, plug in the power adapter. This should "kick start" the figure. Caution: Wear rubberized gloves, you might get a little "kick start" yourself.
The only other thing I can think of is a "short" in the cauldron to witch cable.
something I also did after mine started acting up, was to change the adapter to a universal ac adapter with a lesser voltage. She works fine now!?