You may notice that grid lines in Excel disappear from time to time.  This generally occurs as you are altering the formatting.  If all of your excel grid lines have disappeared, you probably have them turned off.  This solution is for the situation you see here where only some of the grid lines are missing in a workbook.  This is usually caused by cell formatting.  You will notice here that the culprit is actually a cell fill.  The cell fill has been set to white.  The normal setting is no fill.  Select all the cells with no border and set the the fill to no fill and your grid lines should return.  Now you can get back to those formulas and finish your project on time.