I want a powershell script to be run once per minute in the background. No window may appear. How do I do it?
Schedule your task to be run as System. The command below will schedule a script to be run in the background without showing powershell console window:
schtasks /create /tn myTask /tr "powershell -NoLogo -WindowStyle hidden -file myScript.ps1" /sc minute /mo 1 /ru System
/ru
switch lets you change the user context in which the scheduled task will be executed.