How do I reassemble drop-in bobbin case for Brothers XL 2600 free arm?

Sewing Machine: Needle won't move
A disengaged clutch, broken drive belt or internal drive gear failure can prevent the needle from moving. Engage the hand wheel clutch if you have it disengaged for bobbin winding. If the needle won't move with the clutch engaged, unplug the sewing machine and check the drive belt.
https://www.searspartsdirect.com/diy/symptom/sewing-machine-repair/1234596/needle-won-t-move/smac1011147
How to Fix Brother Sewing Machine Error Code E6 Q: What does E6 error message mean? A: The motor locked up because thread is tangled Q: How to fix E6 error message? A: Do the following:

• The upper thread could be tangled. Remove the upper thread and any loose threads. Raise the pressure foot, raise the needle to its highest position and rethread the machine.
• Remove the bobbin and bobbin case to clean any lint or loose threads. Install the bobbin case so that the projection on it aligns with the spring. Then install the bobbin into the bobbin case.
• The needle could be bent. Replace the needle making sure the flat side is facing the back.

***Adjust the top thread. It must be fed through the tension properly. It is best to feed the thread with the pressure foot up. While threading the machine give small tugs to check for stuck areas. Fix these even if you have to replace the thread.
***Don't thread needle yet. Now, Set the pressure foot down. Give small tugs. There should be some tugs. Adjust the tension up and down while doing this to make sure the tension is functioning.
***Thread the needle and set the tension to four. Adjust if necessary as you sew.
That is your problem. However, I've placed a guide how to set the tension of the bobbin.

HAND WHEEL NOT TURNING EASY
If the hand wheel isn't turning freely here are possible problems.
1. Clean bobbin area and ensure bobbin case is inserted properly.
Also, put one drop of oil on race (bobbin case sets on it).
2. Check/remove material from feed dog.
3. Remove the thread and rethread with the pressure foot up while giving small tugs as you go to check for snags.
4. Afterwards put the pressure foot down and give a small tug to check for excessive resistance on thread. It is a good idea to start at four. Now place thread in needle.
5. Put oil on needle arm and pressure foot arm.
6. When done it should work.
7. If this is still a problem the interior of the machine may need cleaned and lubricated.

If the hand wheel isn't turning freely here are possible problems.
1. Clean bobbin area and ensure bobbin case is inserted properly.
Also, put one drop of oil on race (bobbin case sets on it).
2. Check/remove material from feed dog.
3. Remove the thread and rethread with the pressure foot up while giving small tugs as you go to check for snags.
4. Afterwards put the pressure foot down and give a small tug to check for excessive resistance. It is a good idea to start at four. Now place thread in needle.
5. Put oil on needle arm and pressure foot arm.
6. When done it should work.
7. If this is still a problem the interior of the machine may need cleaned and lubricated.

If the hand wheel isn't turning freely here are possible problems.
1. Clean bobbin area and ensure bobbin case is inserted properly.
Also, put one drop of oil on race (bobbin case sets on it).
2. Check/remove material from feed dog.
3. Remove the thread and rethread with the pressure foot up while giving small tugs as you go to check for snags.
4. Afterwards put the pressure foot down and give a small tug to check for excessive resistance. It is a good idea to start at four. Now place thread in needle.
5. Put oil on needle arm and pressure foot arm.
6. When done it should work.
7. If this is still a problem the interior of the machine may need cleaned and lubricated.

try these 2 links
http://www.brother-usa.com/VirData/Content/en-US/HAD/Consumer/UsersManual/UM_CE_5500PRW_EN_2416.PDF

http://www.brother-usa.com/VirData/Content/en-US/HAD/Consumer/QuickSetupGuide/QSG_CE_5500PRW_MULTI_2417.PDF

It is possible that the "shuttle" isn't moving properly. It's also possible that it has a burr. Since it appears that you not little to nothing about these machines I would take it in and have it serviced. Tell the service person about your problem. Ask them to clean, oil, and time it.... and look for issues with parts. it will cost you about $150 or more if it needs parts.

To get that same thread onto the bobbin, you'll need to windit. Here are the steps:1. Removethebobbin from the sewing machine. If your machine has a free arm, you'llhave to remove this first. Open the bobbin door to reveal the bobbin case, forvertical loading models. If your machine has a drop-in bobbin (horizontalloading) you may have to simply slide the metal plate open, which sitsunderneath the presser foot.2. Lift the latchand pull the bobbin case out of the machine (for vertical loaders). Butfor drop-in bobbins, simply lift the bobbin out of the housing.3. Tip the bobbincase over and let the bobbin fall into your hand. (Some bobbin caseshave a latch on the side, that when lifted releases the bobbin). If the bobbinhas another color thread on it, use a new bobbin. Or, if it's not too muchthread, roll it all off and reuse the bobbin. Just make sure the bobbin youwind begins empty. (But in a pinch, you can wind a new color thread over theold color. Just know that you may have to rewind the bobbin fairly soon, as thedesired color thread finishes faster.4. Place yourselected thread onto the spindle and insert a holder over it, if there is one(usually on horizontal spindles only). Many machines just use gravity toretain the thread, so if your spindle is vertical and you have no such part,don't worry about it. If thisis a brand new spool of thread, you may need to free the end. Look for a smallnotch on one end of the spool. You may have to peel back the label a bit to getat it. Then yank it free.5. Loop the free endof the thread over the bobbin tensioner and any hooks on it. Thelocation of this part varies, but it generally looks about like this. Thread the end of the thread through the pinhole in the top of the bobbin. 6. Press the bobbinall the way onto the bobbin winding spindle. Make sure any springs orclips engage. Put it on so that the end of the thread that you put through thepin hole sticks out towards you (or sticks up, depending on if your bobbinwinder is at the top of your machine). 7. Disengage theneedle mechanism. Many machines have this control in the handwheel. It may require a push, pull or twist of the middle of the hand wheel.Check your sewing machine manual to be sure. The sewing machine may run fasterwhen winding a bobbin than when sewing and you don't want the needle moving upand down wildly. Engage the bobbinwinding mechanism. On some machines, it's done by pushing the bobbinspindle over to one side. You may also need to move the stitch selector to abobbin winding position.8. Hold the free endof the thread and, keeping fingers clear of all moving parts, press the footpedal or knee lever. The bobbin spindle will turn. If you have thebobbin threaded correctly, the bobbin will wind smoothly, evenly, and snugly,with perhaps a slight bulge in the middle. You should cut off the end of thethread you were holding in your hand (very close to the bobbin) as soon asthere's enough thread on the bobbin to hold itself in place so it won't slipout. This will prevent this thread from tangling onto any moving parts.9. Fill the bobbincompletely. It may seem like a lot of thread, but you don't wantto run out too soon while you're sewing. Many machines have a built-in deviceto stop winding when the bobbin is full, often a small blade that automaticallycuts the thread when the wound bobbin is full. If your machine has such adevice, let it tell you how much to fill the bobbin. If not, fill the bobbin nofurther than its edges. Hold the bobbinand case so that they are oriented as shown. Check that thebobbin will unwind in the correct direction. If not, flip it.10. Insert thebobbin into the bobbin case. Pullthe thread under the bobbin tensioner (a thin metal latch). The threadshould advance with a little resistance when you pull at it. Allow this excessthread to just hang. Lift the latch onthe bobbin case and hold it as shown.11. Insert thebobbin case into its housing. Make sure it is all the way engaged (youshould hear it click into place) and that the direction is correct. The bobbincase shouldn't spin and shouldn't come loose when you release the tab. Itshould be locked in. And the loose end of the thread should hang free. Do notclose the bobbin door.12. Re-engage theneedle at the hand wheel, disengage the bobbin winder, and set the machine backtoa straight, forward stitch. Thread the machine with the top thread as usual. Once the threadis through the needle, you must raise the bobbin thread. Hold the end of thethread with your free hand. Turn thehand wheel towards yourself. The needle should go down and back up to itshighest position. One full rotation should do it. The top thread will passaround the bobbin.13. Watch as the topthread pulls the bobbin thread up through the hole in the plate under thepresser foot. Pull the looseends to extend them, and continue to hold them firmly so they don't get tangledas you begin to sew.Closethe bobbin door before sewing.Hope this will help you. Good Luck.

No, it seems like you haven't listened for the click of the bobbin locking in place when you put it in.

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.