Stripped gears are the likely cause for the GravityLight to become jammed. Since the gears are damaged and cannot mesh properly, the gears will become stuck. The gears will need to be replaced by removing the front panel and the frame. Instructions on how to access the gears can be found in the Internal Gear Replacement guide.
If neither light is illuminating, then no power is reaching the LEDs or the LEDs have burned out. If no power is reaching the LEDs, then the motor has burned out and will need to be replaced by taking the front panel, frame, and gears out. Steps to remove the motor can be found in the Fixing Post Replacement guide. If the LEDs have burned out, both LEDs will need to be replaced; replacing the LEDs involves removing the front panel. Information on how to replace the LEDs can be found in the LED Replacement guide.
Do not force the dial out of the position the dial is stuck in. To avoid breaking anything, you should follow the Brightness Dial Replacement guide to replace a possibly broken dial, which involves removing the front panel.