quiltingshorttimer makes a good point. If the machine has been sitting unused for a long period of time, it's a good idea to oil and then run it for awhile without thread. I do this with my Voyager periodically, especially if I have not used it for a few months. I oil it, then let it run for 15 minutes at medium speed -- no thread, but with the bobbin in the bobbin case. This distributes the oil through the machine. If it's been a longer time than that, the next day I oil it again and run it again on high speed for about 10 minutes. Note: Since your problem has been jamming of the needle in the down position, I would run it *only* on a slow speed at first. Increase speed only if the jamming problem does not occur.
In any case, this would be a good test to see if the machine runs okay without thread and without a quilt. If it does not stop and jam the way you describe, then it's probably an issue with the needle, thread, or quilt. If the machine still jams with the needle down, then I would suspect that the machine needs to be re-timed.
Incidentally, how tight is your quilt in the frame? It should be relatively loose. The rule-of-thumb is you should be able to push a finger up from below the quilt and be able to grab that finger with your other hand. A quilt that is pulled too tight in the frame can cause problems too.
What type and size needle are you using? It should not be a ballpoint needle, and usually size 90/14 is the smallest you should use.