[Kazun]

1) Использовать Read-Host
2) Указать параметр mandatory

Код:

[CmdletBinding()]
Param(
    [Parameter(Mandatory=$true)]
    $account,
	[Parameter(Mandatory=$true)]
    $al,
	[Parameter(Mandatory=$true)]
    $gname,
	[Parameter(Mandatory=$true)]
    $sname,
	[Parameter(Mandatory=$true)]
    $OrUn,
	[Parameter(Mandatory=$true)]
    $Dep	
)