Pop up reminder

Hello Guys!!!

I'm new here and I need some help with my code, right now i'm trying to have a POP UP Reminder in my excel. and I made the following code:

Private Sub Workbook_Open()
For Each Cell In Range("A2:A100")
For Each Reminder In Range("B2:B100")
If Cell.Value < Date + 3 And Cell.Value <> "" Then
MsgBox ("You Have upcoming Deadline ") + Reminder.Value
Cell.Interior.ColorIndex = 3
Cell.Font.ColorIndex = 2
Cell.Font.Bold = True
End If
Next
Next
End Sub

its already working but the problem is once the Message box show up it will remind you all the deadline and it won't stop showing. can anybody know how to stop the looping of the message, I just need to show it once the workbook is open.

Thanks in Advance,
Ray