Try the following steps:

1. Open the PowerPoint presentation and select 'Slide Show' from the ribbon at the top.
2. Select 'Set Up Slide Show' from the left side of the screen.
3. Check the box for 'Browsed at a kiosk'.
4. Select 'Ok'.
5. Click 'Full Screen'.

If these steps do not work, check to ensure your display resolution is properly set for your computer before trying again.