Powerpoint presentation will not stay in full screen mode

I'm using a Dell LCD projector (2400MP) with my Latitude D820 (running WinXP). When I display my PowerPoint presentation through the projector in full screen mode, the presentation eventually switches back to thumbnail view during the presentation. I cannot get full screen mode to stay. I cannot detect a pattern in timing or otherwise as to why or when this occurs.

 

I've tried a number of workarounds which have not worked, such as: 1. run file from CD or thumbdrive; 2. exit out of spyware and security programs and services; 3. monitored Task Manager to see if any processes ran right before the full screen mode ended to see what was taking the focus from full screen mode; 4. used different versions of the PPT file (.ppt and .pptx).

 

Any further suggestions would be appreciated.