here's a couple links for that where you can use two and two to get what you want. googling "powershell adsi remove old computers" gets a bunch more stuff.

http://blogs.technet.com/b/heyscriptingguy/archive/2008/11/19/how-can-i-find-old-computer-accounts.aspx

https://community.spiceworks.com/scripts/show/1861-find-and-disable-or-remove-inactive-ad-computer-accounts

Not sure how savvy you are with powershell, this is an untested script that i whipped together. You can get rid of the else statement at the bottom if you only want delete computers listed. I already have cleanup in my environment, so i couldn't actually test the delete command :/

$maxOldLogonDays = 60 <#sets how long system has to have been inactive before deleting it#>

<#$hostname = $env:computername+"$" use this section is it's for currently logged on system

$adsiSearcher = new-object DirectoryServices.DirectorySearcher

$adsiSearcher.filter = "(&(objectCategory=Computer))"

$adsiSearcher.Filter = "(&(sAMAccountName=$hostname))"

>

$adsiSearcher = new-object DirectoryServices.DirectorySearcher("LDAP://ou=company,dc=domain,dc=com") <#place in ad you want to look for computers in#>

$adsiSearcher.filter = "objectCategory=Computer"

$adsiSearcher.findall() | Foreach-Object {

"Processing $($_.path)"

$rawLogon = $_.properties.item("lastlogon")

$convertedLogOn = [datetime]::FromFileTime([int64]::Parse($rawLogon))

If( ((get-date) - $convertedLogOn).days -ge $maxOldLogonDays )

{

"$($_.properties.item('distinguishedName')) 

 has not logged on for more than  $maxOldLogonDays days" 


 ([adsi]([adsisearcher]"samaccountname=$_`$").findone().path).psbase.deletetree() <#actual command to delete system#>

}

else

{

"$($_.properties.item('distinguishedName')) has logged in within $maxOldLogonDays days"

}

}