Track Changes In Workbook By User Name

I am unable to add which user made the change to the specific cell. The code used is:

Dim vOldVal 'Must be at top of module
Private Sub Worksheet_Change(ByVal Target As Range)
Dim bBold As Boolean
If Target.Cells.Count > 1 Then Exit Sub
On Error Resume Next
With Application
. ScreenUpdating = False
.EnableEvents = False
End With
If IsEmpty(vOldVal) Then vOldVal = "Empty Cell"
bBold = Target.HasFormula
With Sheet1
. Unprotect Password:="Secret"
If .Range("A1") = vbNullString Then
.Range("A1:E1") = Array("CELL CHANGED", "OLD VALUE", _
"NEW VALUE", "TIME OF CHANGE", " DATE OF CHANGE")
End If..................................................