Could you please tell us what they look like?? are they to loose on the top or bottom if so your tension isn't set right

Re-check the manual to be sure you threaded the machine correctly.

Always thread with the presser foot up - this is important.

Open the manual and follow the instructions for winding and installing the bobbin.

Continue to follow each feature, step-by-step in the manual to fully understand how the machine operates.

If you do not have a manual, you can download a free one, or just view it at Brother.com.