Offizieller Kommentar
Hey Rocio,
If the problem exists on both of the line inputs AND phono inputs, there could be a problem with the internal mixer on the DDJ. Before going to servicing, I'd suggest you test the inputs again with a known-working device.
If you determine it's a problem in the controller, please contact a Pioneer DJ authorized service centre in your region to have your DDJ inspected and/or repaired.