If i haven't any of the NCC certificates.. would it affect my selection?

No it really don't affect your selection because there are usually three stages for the selection in any particular wing of the defence,that is in army,air force,navy.
The stages are
1)Entrance exam 2)SSB(Service Selection Board) Interview 3)Medical Fitness.

CDSE-Combined Defence Service Examination-is a entrance exam which the candidates need to qualify to get in to the next stage that is the interview stage.
Now if you have the NCC certificate,then you will be directly called for the SSB interview,means it will be a two stage process for the NCC certificate holders.