Have a janome master craft 3000, just bought it used yesterday. Was sewing fine then all of a sudden it would stop pushing the material through like the needle was dull or something. Now it's doing it constantly and the material is bunching up and not advancing forward. I already changed the needle. could it be the thread is caught in the bobbin? Or something wrong with feed dogs?

First do a process of elemination. Unthread the machine, both top and bottom, take out the needle. Place a piece of fabric under the pressure foot, lower the pressure, and depress the foot control. Does the fabric feed? If it does, then put in a NEW needle, thread up the machine, and see what happens. A dull needle won't prevent the fabric from feeding. If the fabric does not feed with no thread, then you have a pressure foot pressure problem, or a feed dog height problem, or a feed step motor problem, or possibly a board problem. If it only has a problem when you thread it up, then maybe you have a burr on the needle plate and the thread is hanging up on it and preventing the fabric from feeding. Check for all of these and if you still need assistance respond back.