my fly wheel wont tur on my brother vx1125?

Hi can anyone help i was sewing my curtains when my sewing machine jammed.I turned the big wheel back and forth but can not make it turn a full revolution When i switch to bobbin wind the large wheel and the belt fly round but as soon as i switch back to sew mode the shaft and large wheel turn a tiny amount then it jams.
It is not the shuttle that is clear it seems to be jamming when the spring in tha large wheel clicks back to sewing from bobbin winding. please can you help me.