How can add data into datagridview using button_event

Hi friends,
I have two combobox and two textbox and one button. in button click event I want to add all the date in the combobox and textbox need to add in the datagridview.
I add this by creating datatable and add data to datatable and finally bind this datatable to datagridview. but It only add data in the first row. at every buttonclick event it just add data in the first row of the datagridview,because datable object reference newely created is bind to datagridview. but i want to add data to datagridview as a new row for every button click event. please give me sample available for this issue?
Thanks for advance