Find a Misbehaving USB Device
If Windows tells you a USB device is waking your computer, you’ll have to find the offending device. I’d bet dollars to donuts it's your mouse or keyboard—may be your cat thinks it's a fun toy when you aren’t looking—but it could be anything.
If you have trouble figuring out which device is the problem, remove all your USB devices the next time you put your computer to sleep, and see if it wakes up on its own. If it doesn’t, you can leave one device plugged in the next time you put it to sleep. Keep doing this until you find the offending device.
Once you find the problematic hardware, open the Start menu and search for the Device Manager. Find the device in the resulting list—say, your keyboard—and right-click on it, selecting Properties. Under the Power Management tab, uncheck the Allow This Device to Wake the Computer option and click OK.
From then on, your computer should stay asleep—if not, you might also try entering the BIOS and disabling USB waking from there, if you see an option for it. (You can enter the BIOS setup by pressing a key when your computer first boots, usually something like Delete or F2—the boot screen will usually tell you.)
Limit Your Network Adapter
One of my insomniac computers told me that it was waking up thanks to an Intel(R) I211 Gigabit Network Connection. That’s the Ethernet port that connects my computer to the internet, and it means some sort of network activity is waking the computer up regularly. You can fix this from the Device Manager.
Open the Start menu, search for Device Manager, and find the Ethernet or Wi-Fi adapter in question under Network Adapters. Right-click on it, choose Properties, and head to the Power Management tab. Uncheck the Allow This Device to Wake the Computer option, and you should be golden. You may also find network wakeup options in the BIOS, as described in the USB section above.
Alternatively, you can keep that box checked, and check Only Allow a Magic Packet to Wake the Computer. This is useful if you use Wake-On-LAN to access sleeping computers remotely. It’ll ensure that Wake-On-LAN still works, without allowing just any network traffic to rouse your computer from its slumber. This box isn’t checked by default, for some ungodly reason, and checking it solved my problem beautifully.
Disable Other Wake Timers
If none of the above fix your issue, you may have to dig into the wake timers set on your computer—that is, scheduled events that are allowed to wake your machine. Open the Start menu, search for Edit Power Plan, and click Change Advanced Settings. Head to Sleep > Allow Wake Timers and change both Battery and Plugged Into Disabled. You’ll want to repeat this process for all your power plans in the drop-down box at the top, not just the one you’re currently using.
Here’s the thing, though: this is a sweeping setting designed to affect all wake timers, which may mean it’s too overzealous for you (if you have certain wake timers you want turning on). It’s also weirdly ineffective, which means even if you do want to go nuclear on wake timers, it may not stop them all, but feel free to adjust it anyway.
With that in mind, I also recommend opening PowerShell and running the following command:
This may help you find scheduled tasks designed to wake up your PC. If you find any you want to be turned off, search the Start menu for Task Scheduler, navigate to the task in question using the sidebar, and double-click to edit it. Specifically, uncheck the Wake the Computer to Run This Task box under the Conditions tab.
Random wakeups can be incredibly finicky to solve, and you may find that even more digging is required to find your specific issue. But hopefully, the above options have at least pointed you in the right direction. Keep in mind that you may have to go back and do this in a few months if it starts happening again—new programs, new hardware, and Windows updates can always cause the problem to resurface. It’s a curse, but at least now you can keep it under control.
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