A few people, including me last December, have had this problem with their Octatracks in recent months. The likely problem is that a cable has become detached inside. I sent mine in under warranty for what was probably a trivial repair. I wrote a thread about this but can’t find the link right now.
Everything will be OK.

Edit: this was my thread:
http://www.elektronauts.com/t/elektrons-repair-service/3058/24204