Function Show-Inputbox {
 Param([string]$message=$(Throw "You must enter a prompt message"),
       [string]$title="Input",
       [string]$default
       )
       
 [reflection.assembly]::loadwithpartialname("microsoft.visualbasic") | Out-Null
 [microsoft.visualbasic.interaction]::InputBox($message,$title,$default)


}

$c=Show-Inputbox -message "Enter a computername" `
-title "Computername" -default $env:Computername

if ($c.Trim()) {
  Get-WmiObject win32_computersystem -computer $c
  }