No worries, bringing back the gridlines in Excel 2007 is a quick and easy fix. Here are the steps to follow:

1. Select the entire worksheet by clicking on the box at the intersection of the row and column headers (top left corner of the worksheet).
2. Right-click on any of the selected cells and choose "Format Cells" from the drop-down menu.
3. In the "Format Cells" dialog box, click on the "Border" tab.
4. Under the "Presets" section, select the first option which is "None".
5. Click on the "Outline" button under the "Style" section.
6. Click on the "OK" button to apply the changes.

This should bring back the gridlines to your entire worksheet. If you only want to bring back the gridlines to a specific section, select that section first before following the above steps.