Workbook Macro To Check Empty Cells

I am wanting help regarding excel. I have many cells in different sheets of a workbook. I sometimes have either saved or printed out without realising some critical cells should have been filled but weren't.
I presume I need a macro that will check these critical cells and give a warning with the option of ignoring or filling in the appropriate cells.

Is this possible? Any help would be much appreciated.

Re: Workbook Macro To Check Empty Cells

Depth Thick Purpose No. Length

70 x 35 Strapping (E3) 5400
70 x 35 Ribbon Plate (E4) 5400
70 x 35 B/Veneer Runner 5400
70 x 35 Random 20 5100
140 x 35 Capping
140 x 35 Valley Board
70 x 45 Random
69 x 47 Purlins
90 x 35 Random 1 25000
90 x 45 Random 1 80000

If I print this sheet out or save .xls file, I would like to have a warning that cell E3 and E4 have not got a value.
All other empty cells in column E are ok to be empty or to have a value, but I must have a warning for E3 and E4.

Thanks