script not able to query OS in domain

Hello

I have a script which queries for number of specific operating systems in a trusted domain. Everytime I run this scripts it returns 0 instead of actual count of operating systems. 

$domain=read-host "Please Enter Domain"
$computers= dsquery computer "OU=$domain,dc=$domain,dc=Bigla,dc=bm"		

$Win7 = 0
$WinXP = 0

Foreach ($computer in $Computers) {
    if ($computer.operatingSystem -like "Windows 7*") {
        $Win7++
        }
    elseif ($computer.OperatingSystem -like "Windows XP*") {
        $WinXP++
        }
	else {
        $_
        }
}
$Win7
$WinXP