I suspect most people know how to fix this in Windows, but I think it’s worth a mention. If your computer screen goes black after 10, 20, or 30 minutes, even with the screensaver on, this is due to the Power Options settings turning the signal to the monitor off to conserve power.
This normally shouldn’t happen if the screensaver is enabled, but you or someone else may have changed the settings.
In Windows XP
1. right-click on the desktop, and choose “properties”
2. on the “screensaver” tab, click on the “power” button
3. Choose options from the drop down menus, and click “ok”, then “ok” again.
To change the Power Options, in Windows Vista…
1. In the Start Menu, then select “Control Panel”
2. Click on “Power Options”
3. on the left hand side, choose “Choose when to turn the display off”
4. In the window that opens, choose from the drop down menu the option you want, and click “save changes”