Do you want borders or gridlines to appear on those cells? Borders will print, while gridlines will only appear on screen. If the gridlines have disappeared, go to Tools > Options > View and make sure that Gridlines is checked under Window Options. If the gridlines are still not there, select the cells they're missing from, and select Format > Cells > Patterns and choose No Color.
If it's borders that you want, select the cells you want borders for, select Format > Cells > Border, click on Outline and Inside (assuming you want all 4 borders for each cell) and click OK.
Let me know if you'd like more help,
-Ben
Thanks Ben! I should have been more specific in my question by stating that it was gridlines on the screen I was looking for. The Format > Cells > Patterns, No Color gave me what I needed!