'If Comment does not exist
If Range("B4").Comment Is Nothing Then
Range("B4").Value = "Does not exist."
End If
'If Comment exist
If Not Range("C4").Comment Is Nothing Then
Range("C4").Value = Range("C4").Comment.Text
End If
'Turn Off Screen Updating
Application.ScreenUpdating = False
'Optional: Refresh/Update screen manually when needed
Application.ScreenRefresh
'Your Code
'Turn On Screen Updating
Application.ScreenUpdating = True