Option Explicit
Private Sub Worksheet_Change(ByVal Target As Range)
Application.ScreenUpdating = False
Dim i&, j&
If Not Application.Intersect(Target, Range("d80:x110")) Is Nothing Then
Range("d80:x110").Borders(xlDiagonalUp).LineStyle = xlNone
Range("d80:x110").Borders(xlDiagonalDown).LineStyle = xlNone
For i = 80 To 110
For j = 4 To 24
If Cells(i, j) = "" Then
Cells(i, j).Borders(xlDiagonalUp).LineStyle = xlContinuous
Cells(i, j).Borders(xlDiagonalDown).LineStyle = xlContinuous
Cells(i, j).Borders(xlDiagonalDown).Weight = xlThick
End If
Next j
Next i
End If
End Sub