How can I know someone turned my computer on and used it?

-I'm expecting someone is going to run my laptop and steal or delete some videos, pictures and so on, I thinks there is a way to know the time when my laptop was on, and what has been done, can someone show me how to discover that? I'm using window 7.Yes, and this service is called Event Viewer. You can find it like so:



Start > Control Panel > Performance and Maintenance > Administrative Tools > Computer Management > Event Viewer. Click on System Log.
Just set a boot password to prevent even booting your laptop without your permission, but just make sure to memorize it)), and set a password to your account and nobody will definitely use it
look at the security logs in the event viewer. This will show you what user logged on and when. Also, you should password protect the laptop so this doesn't happen again
Well you could check your history and also just set a password so it doesn't happen again