No sound thru headphones

I have a MacBook. CI2, AI5 Cubase. Headphones are inserted into phones input. Worked at first and now no sound comes through the headphones. Not sure if I changed a setup inadvertently or what. Can anyone help? I’ve looked at everything I could think of. System preferences sound says “no output controls” when I select steinberg C2. Appreciate any help anyone has. Thanks.