It’s time for a public service announcement! If you are one of the few people who are troubled by a PC which randomly and unwantedly wakes up in the middle of the night, or any time for that matter, I’ll show you how to solve these issues once and for all.
First a good idea is to check the Task Scheduler. There is a chance that a program you have installed added a task to the Task Scheduler, and scheduled it to wake up your PC overnight and start doing whatever it needs to do.
Simply go to the Start Menu, type Task Scheduler into the search box and once it opens, click on the Task Scheduler Library. Scroll over to the task last run time and see if there is a task that last run at a ridiculous time such as 3 AM; all it takes is right clicking said task and choosing Disable or Delete to ensure that it never starts back up again.
Now I had a particular issue where my PC would wake itself up at 2 AM every night and there wasn’t anything to be seen in the Task Scheduler. The second thing you can look for is the Wake on LAN (WoL) setting that is available to a lot of network adapters. If WoL is enabled, a device on your network may be erroneously sending a “magic packet” that is turning your PC on.
Luckily this issue can be easily solved. Simply go to the Control Panel and then into the Network and Sharing Center. In the left-hand panel, click on Change adapter settings and all your network-related hardware should be displayed. Then choose the one which you think will be the culprit (which is almost certainly the device connected to your network), right-click and choose Properties and then Configure in the next window. Go across to the power management section and ensure that Allow this device to wake the computer is unchecked. Done.
There is a chance (as was in my case) that this also didn’t solve the issue, so there is one last resort that can be taken. Windows has a handy logging feature that logs what program has turned on your PC and when, so we need to access these logs.
In the Control Panel go to the Administrative Tools and then into the Event Viewer; from there choose Windows Logs and System from the side panel. Now choose to sort the logs by source, which may take some time as there could be tens of thousands. You are now looking for the Power-Troubleshooter source in the list, and once you have found that you need to look for the specific wake-up times in the Date and Time column. To help you search for the right log, usually the time you are looking for will repeat itself or it will be an unusually exact time like 2:00:08 in my case.
Once you have found the log, jump across to the Details tab which should display a path to the program that woke your PC. From here the action you take is up to you because you have found what is causing the issues. You may choose to delete the application in question, uninstall it or change its settings to ensure that it does not wake up your PC for no reason.
So there you have it, your random PC wake-up issues should be solved. If not, you can always scoot over to our forums where someone will gladly help you out if the problem persists.
Update: To add to this, commenter xendrome mentions:
...you can open a command prompt and type "powercfg -lastwake" to view exactly what device caused it to wake last.