My White embroidery machine 3300 won't stitch. There are no issues with the top thread that I can see. The design starts with no issues, as soon as the needle goes down it looks like it doesn't hook the bobbin thread. Thus no stitch, then the machine says, "upper or lower thread cut". I have tried cleaning the bobbin case and rethreading both top and lower threads, but nothing gets stitched.
I'd like to echo the first answer and also add that the needle needs to be matched to the type of fabric. Sometimes the wrong type of needle or even a worn or dull needle can cause skipped stitches. I'd try changing the needle first and if that don't work then by all means take it in for servicing.
I have a White W3300 embroidery machine. It keeps saying that the top or bottom thread is cut, but they aren't. I changed the needle and changed the thread. I cleaned out the bobbin area and rethreaded everything.
Make sure it is set properly for the fabric and pattern being sewn.
Make sure all settings are proper.
Make sure you have right needle size and type for your project.
Use good quality threads.