A situation is possible when a turned off computer turns on by itself, to the surprise and fright of its owner. The reasons for this can be different - software and hardware.
Some network cards support the ability to supply voltage to the motherboard if a special command comes over the network (local or Internet). This technology is called Wake on Lan (WOL). It is very convenient in some cases - for example, in this way you can remotely start a database backup or program update at night.
If you do not like that your computer spontaneously turns on from time to time, check the settings of the network card. To do this, go to the "Control Panel" and expand the "System" node. In the "Hardware" tab, click "Device Manager" and double-click on the "Network Cards" icon. To open the drop-down menu, right-click on the network card icon and select the "Properties" command. See what options are set in the Power Management tab. Uncheck the box next to Allow this device to wake up the computer, if it is checked.
Check the other settings in the "Advanced" tab. If the list of properties contains items Wake from Shutdown, Wake from Frame, "Wake-up capability", select the "Off" option in the "Value" box for them.
In the BIOS settings, you can also set the ability to turn on the computer over the network or bring it out of hibernation ("deep sleep"). When turning on the computer, wait until the prompt “Press Delete to setup” appears on the screen. Instead of Delete, the BIOS developer can assign another key, usually one of the functional ones. In the setup menu, find an item that may be related to WOL technology. Most likely, the title will use the words Wake up, Wake, LAN, WOL. Set these options to Disable.
Some BIOS added the ability to turn on the computer after a temporary power outage in the network. Find the Power on shedule item and set it to Disable.
Perhaps the computer is turned on due to a technical malfunction - for example, due to a short circuit in the power supply circuit of the "Start" button. Examine the motherboard carefully for swollen or leaking capacitors, damaged conductive tracks. Try replacing the power supply - most likely, it is the problem.
