Delphinandrina, did you try re-threading your machine? I have 2 Brother embroidery machines. One is a PE800 that is a dedicated embroidery machine with a 5" x 7" hoop area, and the other is a PE400. The PE400 sews and also embroiders a 4" x 4" area. When I first starting using it, I had trouble with the thread going crazy. After some troubleshooting, I discovered that the thread wasn't seated in the tension disc correctly. As I was threading it, I put a little pressure on the thread as I was running it through the tension discs until I heard/felt a gentle pop. After that it sewed beautifully. I have been using sewing machines since I was a teenager and have used so many different brands and models of machines. I had never had a problem with threading before. Also, bobbin thread needs to be going in a certain direction to be threaded correctly.