Problem: Your pitch to the VCs just went south when your presentation croaked.
Likely Cause: Corrupted files, downed router, incompatibilities on a loaner machine--it doesn't really matter. You don't have time to play detective.
The Fix: If you're brave, go without your slides. The sad truth is that everyone hates PowerPoint, and you'll prove your flexibility and ability to handle setbacks if you forgo the crutch of slides and continue immediately.
If you absolutely have to have a presentation and a quick reboot doesn't help, try OpenOffice.org. If you can buy the time, you can download and install it in 10 to 15 minutes.
Better yet, always pack a spare in case of just such an emergency: OpenOffice.org Portable will run directly from any thumb drive. Just keep a copy of it on a USB drive along with your presentation so you can run it at any time, on any computer.
(Note: A forthcoming alternative is Google Presentations, which is due to join Google Docs & Spreadsheets this summer.)
How to Avoid It Next Time: Come prepared. Bring hard-copy printouts of all slides to use as handouts, and pack the aforementioned OpenOffice.org Portable as a precaution.