You have too many PowerPoint slides
If you have more PowerPoint slides than minutes allotted for your lecture/talk, then you have too many slides. I don’t know how to say it any more plainly than that.
Unfortunately, medical school has made me a harsh critic of public speaking. It’s hard for this not to happen when you spend 20+ hours a week in lectures and different talks. So, if your talk is scheduled to run 50 minutes, then you should absolutely have no more than 50 PowerPoint slides for your talk. In fact, if you want to give a good talk and be memorable, whittle your presentation down to 25 slides. You want to spend some time with each visual cue you are presenting and spend a couple minutes talking about the point made by the image you have chosen. (You chose images/charts/diagrams, right? I can read all day from textbooks, why do I want to look at something you stole from a textbook on a giant screen?)
And this one should go without saying, but unfortunately it must be said–DON’T READ YOUR POWERPOINT SLIDES. I am in medical school. My reading ability has been tested numerous times and found to be sufficient.
And if you really want to be memorable, don’t use PowerPoint. (Although, this might freak out Type A med students who need to have copies of every single word you say, but worth the risk.)