changing cells based on dates

[bartoni]

I have 3 probabilities and associated dates in columns H,K,N. The following rules should take place - If a cell in column H is 2005, a date in a cell in column K should be greater than column H and following on N should be greater than K (and H) .e.g

2005 2006 2007 = correct
2005 2002 2008 = incorrect
2005 2006 2006 = incorrect

How would I write a macro to be able to execute a pop up box if this rule hasnt been followed. I use data validation in these columns by making a custom list i dont know if this helps. I thought it would be easier to create 2 VBA codes - 1 to compare columns K and H and one to compare columns K and N.

Ive had a go but its not working

Private Sub worksheet_CHECKdates()
For MY_ROWS = 2 To Range("H65536").End(xlUp).Row
    If Range("H" & MY_ROWS).Value > Range("K" & MY_ROWS).Value Then
        MY_CHOICE = MsgBox("date error found in column H/K")
    End If
End If
Next MY_ROWS
End Sub

Any ideas?
Thanks