First, consider the operating systems of the windows family. Regardless of the standing you version: XP, Vista or Seven - logging and access to them remained unchanged. Just need to go to the start menu -> control Panel -> administrative tools -> event Viewer. In the window that will provides a detailed log of all important from the point of view of system events: enable or disable the power, sleep mode, system upgrade, etc.
If you have a little of the usual log of events that leads the system, you can use additional software. To complete the task will help programs such as Aida, Everest or HMCW (How Much Computer Works). The latter is particularly interesting in the sense that it allows to obtain the most detailed information on the operation of the system: it runs in the background and keeps detailed statistics of time spent at the computer.
To obtain information about turning off the computer in other operating systems. For example, in Linux you can use the command last. To do this, simply open a terminal and enter the command with the right key:- last reboot - displays the string with the date and time of the last reboot - the last shutdown - the latest information on computer shutdown - last -x - displays the record of changes to the level of execution (runlevel): changes in different power modes and change users.
Don't forget that access to system logs is the privilege of administrator of the computer. Therefore, if you do not have full access to the system, some of the described functions may be available to you.