DIAGNOSIS: The drive coupler—the plastic hex-shaped piece that connects the motor shaft to the blade assembly—is either stripped or broken. This is common if you've tried to crush ice or blend very hard ingredients repeatedly.
FIX: Unplug the unit. Remove the jar and look at the small hexagonal socket in the center of the motor base. If you see a white or black plastic piece that looks chewed up or isn't turning freely when you gently poke it with a finger (be careful), the coupler is damaged. You'll need to replace the motor base.
IF THAT DIDN'T WORK: If the coupler looks intact, the issue might be a seized bearing in the blade assembly. Try manually spinning the blades in the jar (unattached from the base). If they don't turn smoothly or are stuck, the blade assembly needs replacement.
HEADS UP: The BL1210BG isn't designed for heavy ice crushing. For frozen fruit, always add liquid. Using it as an ice crusher will strip the coupler quickly.