There are times when a system wake ups randomly from sleep. If this happens, open a command terminal and run the following command.
The output of this command may provide useful information as to why the system woke. If powercfg does not provide anything useful, your system may have woken up from other reasons. If you own a motherboard manufactured by Intel, try disabling the remote wake capability of the Management Engine. Note, this is not related to wake-on-lan. The Management Engine can be accessed by pressing a key during boot. You may have to enable the capability to enter the Management Engine configuration page through the BIOS settings.