There could be a few reasons why Windows PowerShell keeps popping up. One reason could be that you have a scheduled task set to run PowerShell scripts and the task is triggered by an event or time. Another reason could be that you have an application or script that is configured to run PowerShell scripts that is set to run on startup or when a certain event occurs.
If you are not sure why Windows PowerShell is popping up, you can check the event viewer for any error messages or warnings that may give you a clue as to what is happening. You can also check the scheduled tasks to see if there are any PowerShell scripts that are set to run.