I need some help in Excel for a macro.

A1 Column Heading
A2 Negative value (-2)
A3 Sub total (-2) (Cell locked with formula)
A4 I have a positive value (6)
A5 Sub total (4) (Cell locked with formula)
A6 I have a positive value (10)
A7 Sub total (14) (Cell locked with formula)
A8 Empty (waiting for value)

In A8 when I enter a value 1, I need a pop-up message "THIRD WEEK"
only if A4 and A6 is with positive values. If either A4 or A6 has a
negative value the message should not pop-up.

(if possible the message to read "THIRD WEEK + the heading of the
column" would be prefered)

The chart has a range of A4:F313. The pop-up msg could pop anywhere
within the range, if the above scenario occurs.

I hope I am clear in the above explanation
Your help in creating a macro would be appreciated.

Thanks

FLDS