A typical problem I see with presenters that use Power Point or other computer based presentations is that they forget to reboot before the presentation. Many conscientious presenters practice their presentation just prior to the actual delivery. They use up many of the computer resources before their presentation and when the time comes to deliver the program to the audience their computer crashes.
The other problem I see with computer presentations is that people don't know their equipment well enough or they are using the equipment provided by the meeting planner. You must set your computer so that no screen saver or power savers comes on. You must know how to get your projector out of sleep mode when the introducer goes on forever. Sometimes two computers are attached to the same projector. You must know how to switch between the two when it's your turn to present. Or you may be switching between a VCR and a computer.
The whole point is that you don't want to have your presentation ruined by some simple adjustments that you didn't know about.