This happened to me about a month ago!! It was horrible and took hours to figure out. I have a Brothers machine. When I changed out the bobbin, it did not set tension correctly. Yes, the thread was going thru, and I could see it, but it was kinda swingy( is that a word?) birds nest like crazy, Just keep taking the bobbin in and out, be sure and hold the bobbin in PLACE!!!!!! when ur setting ur thread. and really be careful when u feed it thru the auto-matic tensioner. really follow it thru! It would never work by just feeding it thru with the needle! that thread should be tight before feeding tru the needle/sewing part. If u have a brother machine and u can't get it to work, private message me and I would call u on my cell. PS if ur qa new sewer write down where every thing is set before u start adjusting the tensions!!!!!!