It kinda sounds like a cracked gear to me.... I hope I'm wrong. Can you open the top of the machine? If it's affecting the needle bar, I think, top worm gear. However, I don't even know what the gear system is in that thing. Since you only got one response, I thought I'd throw that out there.
If you've pulled the bobbin area apart and cleaned it, and put it back together, and it's still not sewing, I'd check the top gear system.
Good Luck!