Sleep mode--a setting that keeps a computer running at low power--is useful for people who like to leave their computers always on and ready for use but want to save energy or, in the case of laptops, battery life. Those users who mind their computers going to sleep in the first place, however, can change operating system settings to turn off sleep mode.
Right-click the desktop, and select "Properties."
Click the "Screen Saver" and click the "Power" button near the bottom of the dialogue box.
Change the option next to "System Standby" to "Never" for either "Plugged in" or "Running on batteries" or both if that is what you want. Click "Apply" "OK" and "OK" once again to close the Display Properties dialogue box.
Click the "Start" menu button, and then click "Control Panel."
Click "System and Maintenance" and then select "Power Options."
"High Performance" to disable sleep mode for the computer. The monitor will still go into sleep mode unless you click "Change Plan Settings" and disable all sleep options.
Click "Start," and then select "Control Panel."
Double-click "Power Options."
Select "High Performance" under "Additional Plans" and then click "Change Plan Settings." Change all of the options to say "Never."
Mac OS X 10.7
Click the "Apple" menu, and select "System Preferences."
Click "Energy Saver."
Move the slider for computer sleep to "Never." Do the same with the display slider if you do not want the display to sleep either.