Sandeep,
From what I gather you are declaring cdlist as a newly instanciated variable, but you are not filling it in with any data. Instead you are binding an empty list to your combobox. You need to add a method that returns you a list of ColectorDTO objects. Something like..
cdlist = GetCollectors();
where the function GetCollectors returns a list of CollectorDTO objects it has retrieved from some source of data.