Can you provide a drawing if the circuit: I'm not seeing any ground between the Uno and the 298 module, nor am I seeing 5V on the 298 enable pin. (In which case I'm surprised that one of the outputs is working at all...)
(What do the jumpers you mention do?- do they put 5V on the 298's enable pins? What you have is of course a 298 module, not a raw 298, and we don't all know the specifics of the module, which is an implementation of a well known chip, but it's not just the chip.)