Test the codes below, if it works....
for (int j = 0; j < gv_prod.Rows.Count; j++)
{
string id = ((CheckBox)gv_prod.Rows[j].Cells[0].FindControl("Chk")).Text;
string text = ((TextBox)gv_prod.Rows[j].FindControl("txtid")).Text;
string option = ((DropDownList)gv_prod.Rows[j].FindControl("ddlbrnd")).Text;
FileUpload file = (FileUpload)gv_prod.Rows[j].FindControl("fu");
}