Welcome from Mexico...
I am a "Brother" girl...They are good machines...
How often do you really clean your machine?
Its so important to have them run smooth and to give them all the manteinence they need....
Check well for any tiny loose threads cought in the bobbin (sometimes they are so tiny, its hard to see them but they cause plenty of problems...
Try to rewind you bobbin again and rethread your machine all over again....
Are you using the same thread in the bobbin ? (sometimes it matters too)....
Try also different size stitches....
Good luck ...and don't forget to update us...
:D