Advice 1: How to know the time the computer is turned off

Not so important, are you worried that someone is using the computer without your knowledge, or just don't remember how much it went to sleep after a long RAID in the online game, in any case, to determine time off the computer will help the system logs. Typically the special right to access them is not needed.
How to know the time the computer is turned off
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.

Advice 2 : How to know the time the computer is turned on

For the Windows operating system, there are additional gadgets that displays on your desktop information about the current state of a system, including time of work. However, the OS itself has utilities that allow you to determine the load time. In different versions of their work is not organized the same way, but somehow with their help you can find the time and enable computer.
How to know the time the computer is turned on
If it is necessary to determine the on-time of the computer that is running Windows Vista or Windows 7, then it can be done by using a system component called "task Manager". To run it click a free space on the taskbar, right-click and select in the popup context menu, which is called "task Manager". And you can use the combination CTRL + ALT + Delete.
Go to the Performance tab, and, among other information, look in the section "System" the line "working Time". Subtracting from the current time period specified in this row, you can determine the time the computer is turned on.
Use the utility systeminfo, if you want a method which applies to Windows XP too. This tool works in command line, so it should start with opening a terminal command line. Open the main menu on the "start" button and select "Run" to open the window, run programs. It can do the same by pressing the key combination WIN + R. In the entry field, type cmd, press Enter and the system will give you the opportunity to use a DOS emulator commands.
Type into the command prompt, systeminfo. You can highlight and copy (CTRL + C) the name of the utility here, and then click the right mouse button a black terminal screen and in the popup context menu select "Paste". Then press Enter and the tool will collect information about your system. This process will take a few seconds, and then the terminal screen will display a long table with various data.
Scroll to the top of the table and find the line "system boot Time" - and it will be the required switch-on time. But this line is only in Windows Vista and Windows 7, and Windows XP instead, there is the inscription "the system", so you will need to take the specified time from the current clock.
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