I took out the bobbin case and then the shuttle race. Now I can't remember which one I should put back in first.

Sounds like you are describing the hook. Perhaps the owner's manual would be assistance. We don't know the make/model of your machine so are really unable to help. There are some videos on YouTube that show how to install a shuttle and bobbin case, but machines differ.


Set up the shuttle race for RS2000 Series

Brother LS30 Inserting Bobbin Vertical Shuttle Hook

How to Clean and Maintain your Sewing Machine at Home Front Loading Bobbin
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Look at the race cover... it's got a couple of matching dents in one side where the little plastic "bunny ears" fit into them. The shuttle goes into the race, then the race cover goes over the shuttle, and you move the little plastic bunny ears into position to hold the cover -- the tips fit in the dents.
Then put in the bobbin in the bobbin case.
It's very much like this: http://www.manualslib.com/manual/85659/Kenmore-385-15208.html?page=68

The Activa range is fitted with a light-weight part-plastic hook/shuttle that Bernina claims does not require oiling. However, this does not mean it shouldn't be regularly cleaned and I'd recommend that it is also lightly oiled at the same time. Remove the bobbin case, press the metal lever to the top left of the bobbin door and the black plastic hook/shuttle retainer should pop open so that the hook/shuttle can be removed, or it will just drop out anyway. Use a cotton bud to firmly clean around the inside edge of the hook race (the round piece that the hook/shuttle sits in. Give the whole thing a good clean to make sure any surface grime/fluff is removed. Put a small drop of oil on the running surface of the hook race - the recessed groove around the inside edge, before replacing the hook/shuttle and holding in place by pressing the hook/shuttle retainer back until the securing lever clicks back into place. Rotate the handwheel once to distribute the oil and off you go. Dont overoil but do this regularly and your machine will run much quieter and produce a consistent stitch formation.

Clean out the bobbin area if there are any thread tangles there.

Refer to the maintenance section of the manual - see the configuration of the bobbin case and shuttle race? The bobbin case as an extending arm and the race a notch. When inserting the bobbin case into the shuttle, turn the handwheel so the needle is at it's highest position. Then lift the lever on the back of the bobbin case and insert the cast into the shuttle, arm pointing straight up toward the bed of the sewing machine.

Now thread the machine with the presser foot up - always - and see if the tangling stops.

When you forget to lift the presser foot before threading the machine, the tension control does not open to capture the thread. Then when you begin to sew, the top thread has no tension, and the bobbin thread, which does have tension, pulls the top thread to the bottom in messy loops.

I'd advise against using canned air, because unless you aim it very carefully, you'll most-likely blow the fluff and lint into the machine rather than out, which will lead to long-term poor performance. Use the provided brush to brush out fluff and lint and always make sure you brush it towards you so that it comes-out through the open bobbin door ... never brush away from you otherwise you'll just brush it into the machine. To oil, remove the hook/shuttle, clean the hook race thoroughly and preferably with a cotton bud, making sure that the groove that runs around the inside of the hook race is clean and not full of debris. Put a single drop of the correct Bernina oil into the hook race so that the oil runs around in that groove, replace the hook/shuttle and give the handwheel a turn to distribute the oil. Replace the bobbin case and job done. Now, remember this ... dont wait until your machine comes-up with the 'oil' symbol before you do it again ... you should be cleaning and oiling the hook race every 3-5 bobbins-worth of thread - if you do that, your machine will sound quieter, will produce much better quality stitch formation and will last a great deal longer between services (you do have it serviced dont you ???!!!).

Put the bobbin into the case so the thread is feeding clock wise and through the guide on the case.

Lift the lever to hold the bobbin in place.

Insert the bobbin case into the race/shuttle, still holding the lever out.

Align the finger on the bobbin case with the opening in the race/shuttle.

You may have to turn the bobbin case a bit to the left or right for it to line up.

Once it clicks into place it should work without any further problems.

Just to the left of the bobbin case you will see a small lever. Remove the bobbin case and push the lever and that will release the latch which holds the race cover and shuttle (hook).

Clean well with a toothbrush and place one small drop of oil on the edge of the hook where it makes contact with the raceway. Place the hook back and snap the race cover back on.

You might need to clean the shuttle assembly.

1. Raise the needle bar to its highest position and remove the bobbin case.

2. Push levers sideways of the shuttle assembly and liftshuttle and shuttle race cove out by the center pin.

3. Clean the shuttle race of any lint or small particles of thread with a small brush.

4. Put a drop of oil on the center pin of the shuttle and on the shuttle race.

to reassemble, hold sjuttle by center pin and it carefull into assembly opposit the shuttle driver. Slip shuttle race cover into place. Snap the levers into position.

Occasionally remove the needle plate and clean feed dog with soft brush.

I hope that helps!

the hook driver (still in machine) is 1/2 moon shape. The hook is also 1/2 moon shape. If you set the machine on its back, it's easier. Set the hook 1/2 into the other 1/2 of the hook driver to make a circle. Then put the hook cover on (machine still on its back) with the tabs for the twist locks pointed out. Needle gaurd to the top of the machine. Snap the twist locks in place and viola!
Kent

I had the same problem with cleaning and jamming and this might sound silly, but when you're in the middle of trying to fix it remember to look up see that it is threaded up top. I did everything the pp's suggested and when they didn't work I realized the top thread wasn't still threaded around the tension thing anymore. After rethreading it, it worked fine. But I DID reduce the amount of thread on the bobbin at the same time as Drazil suggested.