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Try the needle in the correct position and affixed in place straightly.
The needle, if it were the wrong size and *if* it were turned around backwards or similarly wrongly affixed, could produce tangling.
Check the thread tensions also - set up as if you were coming to a new machine and had to follow all directions in order to know how to do the threading rightly. Take nothing for granted... the needle breaking may have changed something that you take for granted.
How old is the Brother serger in question?