My Janome did this to me a few months ago. I sent it in to her doc and he found thread wrapped and trapped around the armature hinge. Cost me $35 but she got a thorough cleaning and adjusting at the same time so we're happy. Just do NOT keep trying to run her! A woman in my quilt group did that and gummed it all up in there due to the poly content in the thread she used that the doc almost had to replace the armature!
The doc said to never ever pull the thread backward out of the machine when you change thread color; cut it at the top and pull it down and out. And also to never spin the wheel backward, even for one stitch.
Another cause for jam-ups is the bobbin case could be full of lint. I took a class from Jill Schumacher who drummed it into us to thoroughly clean the bobbin area after every bobbin change.