Reason for Windows turning on

Solution 1:

You could take a look on the eventviewer, go to start and look for it. In the field "System" you could see when something occured, filtering for power-troubleshooter.

Check the powermanagement to define if it's hibernation or sleep-state, in the latter it might be that some devices waked it up. You might see which devices waked it up by typing in the commandline:

powercfg -lastwake

or to see which triggers are set up to wake up:

powercfg -devicequery wake_armed

You might disable the wake scheduler in the gui powermangement.

Perhaps the wake_on_lan tool is active ?

Or perhaps a slightly loose of electric current that might give enough power to the power-button.