A Windows PC that wakes itself from sleep is usually responding to a program, scheduled task, USB device or network adapter. The quickest fix is to identify the trigger before disabling broad power-management features.
PCMag's troubleshooting guide starts with the administrator Command Prompt. The command powercfg -lastwake shows the most recent wake source when Windows recorded one, while powercfg -waketimers lists active timers.
Event Viewer provides another route. Under Windows Logs, filter the System log for Power-Troubleshooter events to see recent wakeups and their reported causes. That evidence can point toward one of the narrower fixes below.
Check maintenance, devices and networking
Windows Update can wake a computer for scheduled work. Adjusting Active Hours or pausing an update may help, while Pro and Enterprise editions also expose a Group Policy setting for Windows Update power management.
Automatic Maintenance has its own permission to wake the computer. Windows lets users change its daily time or clear the option that allows scheduled maintenance to wake the machine.
If a mouse, keyboard or another USB device is responsible, Device Manager can revoke that device's wake permission. Testing with peripherals disconnected can help identify the culprit. Network adapters have a similar setting; users who need Wake-on-LAN can restrict wakeups to a magic packet rather than disabling the feature entirely.
Use global wake settings carefully
Windows power plans include an option to disable wake timers on battery and while plugged in. That setting affects every timer and can block useful scheduled activity, so it is a later step rather than the first one.
PowerShell can list scheduled tasks configured to wake the PC with Get-ScheduledTask | where {$_.settings.waketorun}. Individual tasks can then be changed in Task Scheduler. New software, hardware or updates can reintroduce the problem, which is why recording the actual wake source is more durable than switching off every mechanism at once.
