There is nothing wrong with going to an authorized Janome dealer and ask for guidance as to what could be wrong with the machine. You will save yourself headache by learning the proper way to use the attachments and how to run the machine.
I have a Janome 1600P for three years now, and when it started acting up I brought it to be serviced - right there and then the technician pointed out what was going wrong and showed me how to properly thread it and the correct needles to use.