By default PowerPoint will show a list of slide thumbnails on the left of the powerpoint editor, unless you close the pane. If you are trying to recover the list of Slides on the left using powerpoint 2010 but no Slides are displayed there, then here we will try to help you to show this pane with miniature Slides on the left of powerpoint editor again.
You can also learn from this Question in SuperUser where someone asked the same question how to display the list of Slides on the left of powerpoint. You can easily click on View -> Normal view many times to show up the pane on the left. This will display the Slides and Outline tabs.
Alternatively you can drag the splitter from the left to any desired location as shown in the figure above.
This applies to powerpoint 2007, powerpoint 2010 and powerpoint 2013. Using the Slides pane on the left let you manage the powerpoint Slides easily for navigation and cut and paste tasks. The same applies if you want to display the powerpoint Outline pane.