run task in the background

i have powershell script that check if the service is up and of not it starts it up,

$ServiceName = 'mapguideserver3.1'
$arrService = Get-Service -Name $ServiceName

while ($arrService.Status -ne 'Running')
{

    Start-Service $ServiceName
    write-host $arrService.status
    write-host 'Service starting'
    Start-Sleep -seconds 60
    $arrService.Refresh()
    if ($arrService.Status -eq 'Running')
    {
        Write-Host 'Service is now Running'
    }

}

i tried to use it in a task scheduler as system startup and right click and run , by setting "allow it to run on demand"

i saw that the task status is "running" and after some time it changes to "ready", when i checked after some time the task doesn't changes back the service if its stopped.

how can i run the script that it will run forever?