Popup Reminder Excel 2010

I am completely new to VBA and do not really know how to manipulate a code.
I was hoping someone would be willing to formulate the codes I need to input into the VBA box.

I have a sheet for appointment dates at a clinic.
They have dates for each patient as below:

Name First Visit Appt 1 2nd Visit Appt 2 3rd Visit Appt 3 .... 10th Visit
x x/x/x x/x/x x/x/x x/x/x x/x/x x/x/x x/x/x
x x/x/x x/x/x x/x/x x/x/x x/x/x x/x/x x/x/x
x x/x/x x/x/x x/x/x x/x/x x/x/x x/x/x x/x/x

I would like a reminder to pop up everytime the appointment date is past 7 days and the patient has not shown up.

example: today's date is 10/9/15

Name First Visit Appt 1 2nd Visit Appt 2 3rd Visit Appt 3 .... 10th Visit
A 6/3/15 7/4/15 7/4/15 8/16/15
B 9/10/15 10/10/15
C 7/10/15 8/11/15 8/11/15 9/15/15 9/15/15 10/1/15

Patient A was last due on Aug 16, 2015 for her 2nd appt (3rd visit), but it has been close to two months since that appointment.
Patient B is OK, so no popup is needed
Patient C is also past 7days from her appointment 3 date.

I would like a popup window to show up for patient A and patient C with a text of "call to remind".

And if possible, disable specific popups (for example, I see reminder for patient A, and I remind the patient already, so there is no need for me to see that patient A needs a reminder any longer)

What would be the best way of doing this?

As the excel gets filled up with more patients, there will likely be more patients who need reminders, therefore more popup windows when the excel is first opened.

Any help would be much appreciated.
Thank you in advance, and please let me know if there is any other info i should provide.