It is sometimes interesting to know since when your computer is on.
To find out, nothing more simple. Just open the task manager :
- In Windows XP and earlier : by pressing CTRL + ALT + DEL
- On Windows Vista and later either by the above keys combination and clicking "Task Manager". Either by right-clicking on the clock in the taskbar and then clicking on "Task Manager".
Once the "Windows Task Manager" is open, go to the "Performance" tab and look under "Active". In the picture you can see that our computer is turned on for 58 minutes and 10 seconds.