As Om Prakash said, you should put this code in
Form_Load
or
Control_Load
event.
Just like,
Private Sub Form1_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
cbo_StartYear.Items.Clear()
Dim currentYear As Integer = Date.Now.Year
Dim i As Integer
For i = 2009 To currentYear
cbo_StartYear.Items.Add(i)
Next i
cbo_StartYear.SelectedIndex = cbo_StartYear.Items.Count - 1
End Sub