Those slide plate screws can be a problem. Go to Harbor Freight and get a little ratchet off set screwdriver for a couple dollars. Those work the best. A more expensive fix it to find a real nice long screw driver and grind it at an angle. You might need to spend some time reading Rain's blog:
http://vssmb.blogspot.com/ you may need to join the Bernina Yahoo group, too. If you are a beginner, you need to be working on a simple old black Singer sewing machine before you tackle a Bernina.