AssetService not working ?

I use the dell AssetService to get Warranty Info in a Powershell Script.

$AssetService = New-WebServiceProxy -Uri "http://xserv.dell.com/services/AssetService.asmx?WSDL";
    $ApplicationName = "AssetService";
    $Guid = [Guid]::NewGuid();
    $Asset = $AssetService.GetAssetInformation($Guid,$ApplicationName,$ServiceTag);

Actual i get this message :

"The request failed with HTTP status 503: Service Unavailable."