Find what computer a user is logged into

Add-PSSnapin Quest.ActiveRoles.ADManagement -ErrorAction SilentlyContinue
$ErrorActionPreference = "SilentlyContinue"

Function Get-Username {
$Global:Username = Read-Host "Enter username you want to search for"
if ($Username -eq $null){
Write-Host "Username cannot be blank, please re-enter username!"
Get-Username}
$UserCheck = Get-QADUser -SamAccountName $Username
if ($UserCheck -eq $null){
Write-Host "Invalid username, please verify this is the logon id for the account"
Get-Username}
}

get-username

$computers = Get-QADComputer | where {$_.accountisdisabled -eq $false}
foreach ($comp in $computers)
{
$Computer = $comp.Name
$ping = new-object System.Net.NetworkInformation.Ping
$Reply = $null
$Reply = $ping.send($Computer)
if($Reply.status -like 'Success'){
#Get explorer.exe processes
$proc = gwmi win32_process -computer $Computer -Filter "Name = 'explorer.exe'"
#Search collection of processes for username
ForEach ($p in $proc) {
$temp = ($p.GetOwner()).User
if ($temp -eq $Username){
write-host "$Username is logged onto $Computer"
}}}}