Why Do My Computer Lights Turn on When It's in Sleep Mode?

Sleep mode puts your computer into a low-power state, ready to be woken when you want to resume work. The computer lights back up when it awakens. Various things can wake a computer out of sleep mode, including scheduled tasks and other devices or pieces of hardware requesting access to it.

Running Tasks

Even if your computer dozes off, it will wake up if the hard drive initiates a previously scheduled task. These types of tasks include defragmenting, searching for Windows Updates and running anti-virus scans. Unless you specifically tell each of these programs to not wake the computer to run, they'll do just that. You can adjust this in the program's settings or check the Task Scheduler for a list of what may be waking the computer. Select one of the scheduled tasks and check when it's scheduled to run. If it runs at a time when the computer typically sleeps, change the time to prevent it from waking the computer again. You can also open Control Panel, "Hardware and Sound" and "Change When the Computer Sleeps." Select "Change Advanced Power Settings." Expand the "Sleep" entry, and disable the "Allow Wake Timers" option.

Mouse and Keyboard Issues

Wireless or optical mice and keyboards can be a bit quirky, and the flick of a light switch could make either device wake the computer. USB connected input devices can trigger wake up if they're bumped or pressed accidentally. Outdated drivers can also cause communication issues between the keyboard, mouse and computer, waking the computer as it tries to correct it. Update all drivers for your keyboard and mouse, and keep lights away from the sensor on optical mice.

Power Settings

The computer's power settings determine when it goes into sleep mode and what can wake it up. Open the Power Options dialog and click "Change Plan Settings," then "Change Advanced Power Settings." In the new window select "Change Settings That Are Currently Unavailable." This enables you to change the various settings that tell the computer what to do when it goes to sleep. Set the PCI Express to off, USB Settings to disabled and Multimedia Settings to "Allow the Computer to Sleep." This will prevent unwanted waking of your computer when it dozes off.

Device Waking

External devices can wake the computer during sleep mode, the most well-known being the keyboard and mouse. But other hardware can trigger the computer awake, including the router, networking card and printer. Check these devices under Device Manager by selecting the device and right-clicking and selecting "Properties." Deselect "Allow this Device to Wake the Computer." Check every device connected to the computer for this option, such as scanners, printers and routers.