This is usually caused by PowerPoint changing the screen resolution when you go live with the slide show. Make the following setting changes to PowerPoint to correct the problem.
1. Open the Microsoft PowerPoint program.
2. Click the Slide Show Menu or Tab.
3. For PowerPoint 2003 or older, click Setup Show.
4. Change the Resolution to Use Current Resolution.
Also make sure that the PREVIEW WINDOW IS NOT ENABLED as this will break DIRECTX and cause the same thing to happen.