Check if the upper thread is tangled. Remove the thread completely from the machine.  Check the correct size spool cap is being used for the size of the thread spool. Re-thread the machine according to the directions in the manual.

Remove the bobbin and make sure the bobbin is threaded correctly in the shuttle race.    Remove any loose threads or lint in the shuttle race.

Check if you are holding the needle thread too tight. Hold the thread lightly to keep the end from going down into the shuttle.

Check the needle is threaded correctly. Thread the needle eye from the front to the back.

Check if the needle is bent or incorrectly inserted. Install a new needle with the flat side of the needle facing the back.