This is going to strain my powers of description. It's a behavior that drove me crazy and took me forever to diagnose, describe, and find a resolution for. Maybe I can help one other person out there who is similarly perplexed.
Please note that this applies only to Windows, so if you have a Mac, stop reading now.
SETUP: You have two monitors hooked up to your Windows computer. You are showing content on Monitor 2 and running the rest of your controls on Monitor 1. An example situation would be showing a PowerPoint slideshow on Monitor 2 while you share that screen. Monitor 1 has your presenter view and your web conferencing controls.
SYMPTOM: You are working away, clicking items and moving your mouse. Suddenly Monitor 2 goes completely blank! You are still sharing your screen, but there's no presentation on it. You panic and move your mouse around. The presentation mysteriously comes back. You don't know what happened or if it might happen again.
CAUSE: You got zonked by a feature called Aero Peek. You didn't realize it, but you moved your mouse into the taskbar on top of a task icon. That made Windows display a little preview window just above the task icon. Then you managed to nudge your mouse into the preview rectangle. Windows assumes you want to see that task's full window more clearly. So it blanks out everything else on your computer to show you that one window. Poof - Your slideshow display disappears. When you panic and start moving your cursor around again to click on things, Windows restores your content to the previous, normal display. It all happens so fast you can't track the sequence of events. It's just a mysterious, unexplained intermittent behavior.
FIX: You need to get to "System Properties" in Windows. Click here for a list of ways to access that panel. If you find yourself on the main System summary page, click on "Advanced system settings" to bring up the System Properties menu.
Click the "Advanced" tab in your System Properties.
Click the "Settings…" button associated with "Performance"
Make sure you are on the "Visual Effects" tab
Click the radio button selector for "Custom" and uncheck the box next to "Enable Peek"
That's it! OK your way back out of everything and test it. You don't have to reboot.
I'm a lot happier knowing that my presentation won't suddenly disappear in the middle of a screen sharing session. Maybe you'll find it useful as well.