Private Sub ComboBox1_GotFocus()
    Dim arr() As String, j, sh As Worksheet
    j = 1
    For Each sh In Worksheets
        ReDim Preserve arr(1 To j): arr(j) = sh.Name: j = j + 1
    Next sh
    ComboBox1.List = Application.Transpose(arr)
End Sub

Private Sub CommandButton1_Click()
On Error Resume Next
Worksheets(ComboBox1.Value).Visible = True
End Sub

Private Sub CommandButton2_Click()
On Error Resume Next
Worksheets(ComboBox1.Value).Visible = True
End Sub