What should you do when you have committed a huge blunder while giving a PowerPoint presentation or a talk?
For starters, you have to make a quick assessment. Is it noticeable to anyone else? Sometimes you can make a blunder and realise that is not what you wanted to do but no one else has noticed. I want you to be a real human being but I do not want you to just let it all hang out and cry and whine about yourself because if you complain about a mistake, chances are that might be the only thing anyone remembers from your presentation.
I remember it raining that took place that I conducted more than a decade ago. An executive on a military base was giving a presentation over PowerPoint. Everything was going well but at one point his slide froze. He tried to advance it but it was not working. Finally, in a peak of frustration, he slammed shut the laptop, laughed, and continued. Afterwards, everyone said that it was a great presentation and that they loved when he slammed the computer down and kept on going. They could not remember the messages of the presentation because that act of frustration had become the most memorable moment of the presentation.
That is not what you want. You want the memorable parts of your presentation to be on what you are saying. What I would do is divert the attention of the audience from the particular issue at hand. I would continue talking, walk around the room, and toss a question out to an audience member. While everyone is busy looking at that person, I would reach down and plug in my laptop again or troubleshoot it.
So if you have not made a factual mistake, do not beat yourself up about it. No audience in the world is smart enough to read your mind or your outline so do not worry for the smaller blunders as your messages should be the most memorable moments that you put a spotlight on.