Powershell login script to web

I'm working on Powershell script. I want when I execute script to do: 1. Open webpage 2. Bypass warning screen on page 3. Click to Login button 4. Select first certificate & enter PIN & login

Code:

$pin = "666666"
$web = Get-Random -Input https://xxx.sk, https://yyy.sk, https://zzz.sk

$ie = New-Object -ComObject 'internetExplorer.Application'
$ie.Visible= $true
$ie.Navigate("$web")
while ($ie.Busy -eq $true){Start-Sleep -seconds 1;}   

#bypass warning 
$warning = $ie.Document.getElementByID("overridelink")
$warning.click()
while ($ie.Busy -eq $true){Start-Sleep -seconds 2;} 

$login=$ie.Document.getElementByID("LoginButton") 
$login.click()
while ($ie.Busy -eq $true){Start-Sleep -seconds 2;} 

if($(Get-Process | Where {$_.MainWindowTitle -match "https*" -AND $_.Name -match "iexplore"}))
{ 
    #Select first certificate and enter OK
    [void] [System.Reflection.Assembly]::LoadWithPartialName("'System.Windows.Forms")
    [System.Windows.Forms.SendKeys]::SendWait("{ENTER}")
    Start-Sleep -seconds 5

    #Enter a PIN and enter OK
    [System.Windows.Forms.SendKeys]::SendWait("$pin")
    Start-Sleep -seconds 5
    [System.Windows.Forms.SendKeys]::SendWait("{ENTER}")#
}

else
{
    Write-Host "*** Internet Explorer is not running. ***"
}

Everything works fine until selecting certificate and enter pin. There is a problem. Script can't select certificate. I want execute script on background while I will do another things... Title of pop up window is Windows Security

Thanks for help.