The number one challenge for every Sys Admin is to ensure that old computer accounts within Active Directory (such as servers, user PCs or laptops) can be identified and removed. A quick look at the Object tab of a computer account will tell you when the update sequence number (USN) was updated, but not the last time the computer logged into the domain.
There are a couple of ways to identify whether a computer account in Active Directory is stale.
1) Automatically – Setting up a GPO to to automatically identify and remove stale computer accounts ( Use it on your own bed risk approach because you may experience problems with Remote Systems such as laptops that haven’t showed up for a while in the corporate network ).
2) The Manual way – Using the query-command called “dsquery”. Open CMD prompt or Powershell and hit “dsquery computer -inactive 1” ( 1 stands for the number of weeks, which in your case )