I love my machine and have had it for several years and it has made umteen quilts! Jean quilts, poly, slippery throws, cotton hi loft, low loft etc.
You might check if it is threaded correctly, buy the best thread you can afford, I only use Janome bobbins and then I throw the bobbin away after about 5 times it has been filled. The bobbins are plastic and my thought is that they will stretch after alot of use. The bobbins are inexpensive and I get a whole bunch I think about 20 or so per package.
If you bought the machine from a Janome dealer take it back for adjustment or instruction. With this machine it does so many things you really need to take the class to see all it's workings.
Sorry you are haveing the problem - it has been a work horse for me and I have had 7 Janome machines and would not have another brand.
You should have a warrantee but remember the warantee is only good if you use a certified Janome repair.
I sure hope all these suggestions help and I hope you will soon be stitching happily along.