Well, just take it to your LBS (Local Bike Shop) and let them fix it for you. It sounds like all it needs is for the chain to be unjammed and put back on the gears, and, if that's so, then it shouldn't cost much, maybe only, like 5 bucks or so.
Be aware, however, that they will try to sell you a new chain or even a whole new bike so, be prepared to have someone do the whole salesman thing on you when you bring it in to be fixed because local bike shops are hurting right now in this economy so they try to make a sale whenever they can.