Your Pfaff Grand Quilter was built by Janome. Try to find a Janome dealer or service center and see if they can fix it for you. The shaft you are talking about is called the Needle Bar. If it is loose and swivels around I definitely would NOT use the machine. Is finishing a quilt more important than risking a serious injury or at the least, severe damage to the machine if that bar drops out while you are using it.
The nose cover should come off the machine to change the light bulb. If you can get it off you can get to the needle bar.