Exercise Equipment Repair Questions? Ask a Technician
Try setting the bar to 5lb on both sides and remove the handle, leaving all the weights in the base.
Then remove the weights from the base one by one. Once the base is empty, replace the empty handle onto the empty base and try to turn the knob again.
If it still doesn't turn then the block will need to be disassembled to carry out a mechanical repair.
Reply back and let me know how you get on...