If you need to find out who has logged onto a computer, there is a great freeware utility called WinLogOnView that can help you.
WinLogOnView is portable tool that scan the security event log of Windows operating system, and detects the date/time that users logged on and logged off.
For every time that a user log on/log off to your system, the following information is displayed: Logon ID, User Name, Domain, Computer, Logon Time, Logoff Time, Duration, and network address.
WinLogOnView also allows you to easily export the logon sessions information to tab-delimited, comma-delimited, html and xml file.
Windows Vista/7/8/2008. Both 32-bit and 64-bit systems
License : Freeware
Link : WinLogOnView