Auto Drop Down ComboBox

I have a table where I will be entering mass amounts of data. One of the columns contains a data validation listing and I created a macro to assign a combo box to appear where there are data validation drop down lists. Currently, the combo box will open only when you double click on the cells within that column. I would rather have the combo box appear, so when you are tabing across the columns the combo box automatically opens up. Similar to if you are registering on a website and tabing through the different input boxes and get to say birth month and you can then use the down arrow to select your month.

The reason for using a combo box instead of a simple data validation drop down list is I wanted more controls and variations with the combo box. If it helps I'll paste the macro for reference. It is just annoying when I'm tabing across and then you get to the column where I have the combobox assigned and you have to double click in the cell to get the combo box to appear.

Private Sub Worksheet_BeforeDoubleClick(ByVal Target As Range, _
Cancel As Boolean)
Dim str As String
Dim cboTemp As OLEObject
Dim ws As Worksheet
Set ws = ActiveSheet

Set cboTemp = ws.OLEObjects("TempCombo")
On Error Resume Next
With cboTemp
'clear and hide the combo box
.ListFillRange = ""
.LinkedCell = ""
.Visible = False
End With
On Error GoTo errHandler
If Target.Validation.Type = 3 Then
'if the cell contains a data validation list
Cancel = True
Application.EnableEvents = False
'get the data validation formula
str = Target.Validation.Formula1
str = Right(str, Len(str) - 1)
With cboTemp
'show the combobox with the list
.Visible = True
.Left = Target.Left
.Top = Target.Top
.Width = Target.Width + 5
.Height = Target.Height + 5
.ListFillRange = str
.LinkedCell = Target.Address
End With
cboTemp.Activate
'open the drop down list automatically
Me.TempCombo.DropDown

End If

errHandler:
Application.EnableEvents = True
Exit Sub

End Sub

Private Sub Worksheet_SelectionChange(ByVal Target As Range)
Dim str As String
Dim cboTemp As OLEObject
Dim ws As Worksheet
Set ws = ActiveSheet
Application.EnableEvents = False
Application.ScreenUpdating = True

If Application.CutCopyMode Then
'allow copying and pasting on the worksheet
GoTo errHandler
End If

Set cboTemp = ws.OLEObjects("TempCombo")
On Error Resume Next
With cboTemp
.Top = 10
.Left = 10
.Width = 0
.ListFillRange = ""
.LinkedCell = ""
.Visible = False
.Value = ""
End With

errHandler:
Application.EnableEvents = True
Exit Sub

End Sub
Private Sub TempCombo_KeyDown(ByVal _
KeyCode As MSForms.ReturnInteger, _
ByVal Shift As Integer)
Select Case KeyCode
Case 9 'Tab
ActiveCell.Offset(0, 1).Activate
Case 13 'Enter
ActiveCell.Offset(1, 0).Activate
Case Else
'do nothing
End Select
End Sub