Janome MB-4 problems

I just bought a used Janome MB-4 from ebay. Every since I have had this machine I have had issued with getting loose threads on top. Now a month into this machine the tension bar wont work for number 3 and 4 needle. Could that be why I have the loose threads? I have been adjusting the tension up and down and nothing seems to work. Anyone know how much a repair like this would cost? This is frustrating cause I spent about 4k on this machine

your machine should be under warranty. Janome provides 1 Year on the MB-4.

Your Head is jammed that is why you cant use needle 3 and 4 . Janome should look after it for you. You would just have to pay the shipping to New jersey. I would call the first to complain.