1st I rethread, after I run a paint brush thru the bobbin area. Check to see if there are any stray threads stuck around the bobbin race. They like to hide! 2nd I wind a new bobbin. After that ,Ii walk away and come back in the morning or in an hour. What kind of fabric/thickness are you working with? Could be you need a BIGGER needle. I had to change to a topstitch needle this week when I was making a tote. The seams got too thick for my go-to piecing needle. When I went back to piecing? I noticed the needle was having a hard time piercing the fabric. I had forgotten to take the top stitch needle out!