We all know this kind of a nasty situation - a family member or a roommate uses your computer without any permission. You know it's him or her, but you prefer not to talk about it because you aren't sure. However, with a couple of Windows tools it becomes very easy to bring proof to the judge.
Your first steps should lead to your system log. Choose the Control Panel from the Start Menu, go to Administratve Tools, and click on Computer Management.
You can find the most useful information in the Security log, as Windows registers all the logs (system boots) and log-off (shutdowns). By comparing the given hours with the time you remember you used the computer you can easily check if someone used your PC.
In the Application tab you can find information about the activities of users - what programs he or she launched, if they searched the hard drive for something, and so on. Another way to chec if someone used your computer is by browsing the list of recently opened files - you can find it in the Start Menu in Recently used documents.
Of course, this feature won't bring anything new if you have it disabled, the intruder opened no files, or you simply don't remember how that list looked the last time you launched your computer.
Another good way is launching the Windows Explorer and searching all the files that have been modified in a specific period of time (meaning the time you didn't use the computer). Just opening a file also counts as a modification to the system.
If such actions don't bring any results you may also check if someone used your Internet browser - just take a look at the browsing history. Remember, however, that you friend or sister could have cleared the browsing history or used the incognito mode.
Windows can also create alerts that notify you about a computer launch. You can use the Task Scheduler - it will send you an e-mail on a provided address that the PC has been launched.
Such a solution has, of course, some drawbacks - you will receive an e-mail always, regardless of the real user, so you will be notified that you have logged in.