Code:
Private Sub Text1_KeyDown(KeyCode As Integer, Shift As Integer)
   'This is critical - KeyPreview MUST be set to True
    If (Shift And vbCtrlMask) = vbCtrlMask And KeyCode = vbKeyA Then
        Text1.SelStart = 0
        Text1.SelLength = Len(Text1.Text)
    End If
End Sub