Send message to all computers in domain

Hello everyone

I am desperatly trying to find a way to send a pop-up message to all computers in our domain

I wanted to do this via our AD controller, which is a windows server 2012 R2.

I found a Powershell script, but this throws an error at me (see below)

get-ADComputer : The supplied distinguishedName must belong to one of the following partition(s): 'DC=intranet,DC=stekene,DC=be ,CN=Configuration,DC=intranet,DC=stekene,DC=be , CN=Schema,CN=Configuration,DC=intranet,DC=stekene,DC=be , DC=DomainDnsZones,DC=intranet,DC=stekene,DC=be , DC=ForestDnsZones,DC=intranet,DC=stekene,DC=be'.
At line:1 char:2
+ (get-ADComputer -SearchBase "OU=Computers,DC=intranet.stekene,DC=be" -Filter *). ...
+  ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : InvalidArgument: (:) [Get-ADComputer], ArgumentException
    + FullyQualifiedErrorId : ActiveDirectoryCmdlet:System.ArgumentException,Microsoft.ActiveDirectory.Management.Comm

the powerscript  itself is:

(get-ADComputer -SearchBase "OU=Computers,DC=intranet,DC=stekene,DC=be" -Filter *).Name | Foreach-Object {invoke-Command -ComputerName $_ {msg * "text of message" }}

I am not particularly familiar with Powerscript, so I have no clue where to look to correct this ..

In AD the computers are on this level
               Begane grond
               Eerste verdieping
               Externe PCs

Is there anyone who can help?

Perhaps the structure of the OU is causing the problem? Could this be rectified by reading all computernames from f.i. a txt file ? and if so, can someone point out how to do this.

I guess it should be fairly simple for someone who knows Powershell ?.

Thanks a million (below is a screenshot of our AD)