"At times, it is necessary to stop the presentation and resume after a short break. If the PowerPoint presentation is not completed, how can I, as the presenter, do other things during the break and then resume the slide show at the same slide that was on screen before the break, without starting the presentation all over again?"
This is a two part answer. First the presenter wants to pause the slide show and then use his time to work on another presentation or other program while the audience is on a break.
There are times when you will want to pause your PowerPoint slide show during your presentation. The most common reason is that a member of the audience asked a really good question, and you would like to encourage the audience to participate in the answer. You would want to pause the show at this point.
Methods to Pause a PowerPoint Slide Show- Press the B key on the keyboard. This pauses the show and displays a black screen, so there are no other distractions on screen.
- Press the W key on the keyboard. This pauses the show and displays a white screen, so there are no other distractions on screen.
- If the slide show has been set with automatic timings, during the show, right click on the current slide and choose Pause from the shortcut menu. This pauses the slide show with the current slide still on screen.
- Press the B key on the keyboard. This resumes the slide show from the last slide shown.
- Press the W key on the keyboard. This resumes the slide show from the last slide shown.
- If the slide show has been set with automatic timings, right click on the current slide and choose Resume from the shortcut menu.
Work on Other Programs While the Slide Show is Paused
To access another presentation or program while your slide show is paused, use Alt + Tab Fast Switching to quickly switch to the other task. When you are ready to resume your presentation once again, use the Alt + Tab method to return to your paused presentation.
Presenter Tip - If the audience needs a break from the slide show, this a good indication that the presentation is too long. A good presenter will get his message across, in most cases, in ten slides or less. You want to retain the audience's focus throughout the whole presentation.
For more presentation tips, see How to Lose an Audience in 10 Easy Ways. Tip #8 addresses the issue of too many slides.

