problems starting DAF 45 130 L reg?

My horse lorry will not start, I have fully charged both batteries but when you try to start it does not crank, all the lights on the dash are on and the air tanks buzzer sounds. I checked the headlights and they are bright as well, even used jumpleads to give a little help but same problem. both batteries were replaced in October. any ideas on what may be the problem
thanks