If you need to see when a computer last logged onto your domain, here is a quick command to achieve that using PowerShell Active Directory shell:
Get-ADComputer -identity [COMPUTER NAME] -Properties * | FT Name, LastLogonDate
To look at all computers in your network. Change the -Identity switch for the -Filter switch:
Get-ADComputer -Filter * -Properties * | FT Name, LastLogonDate -Autosize
Check out this article to learn more and expand this type of inquiry.