Computer "sleep" settings place monitors and computers (central processing unit, hard drive) into a low-power mode after a certain period of inactivity. Touching the computer's mouse or keyboard will "wake up" the computer when you return.
How to:
Microsoft Windows 2000 | Microsoft Windows XP | Microsoft Windows Vista
Note: If you are on a network, we recommend that you contact your IT Manager to ensure that your computer can still receive network updates. Energy Star provides a web page dedicated to Public Domain/Operating System Solutions for Ensuring that Sleeping Computers Receive Updates.
If you access your system remotely, read this note from Energy Star about which settings to enable.
Resources:
Energy Star - Power Management
Success Stories:
General Electric, Verizon, Dell, Yale University, and University of Wisconsin - Oshkosh are among Energy Star's computer sleep setting success stories.
For more energy efficiency tips, check out Quick Tips for Energy Efficiency.