Running hidden power shell

I am trying to run a script, and I can't have a powershell window pop up for it.  I am trying to use the -WindowStyle Hidden when starting, but it is not working for me.  I am using Win7 x64.

To test, I hit Win + R, and in the Run box, I type:  powershell -WindowStyle Hidden my_script.ps1

And when I hit Enter, Powershell window pops up. 

If I try to just run powershell.exe -WindowStyle Hidden

without any script, a new powershell window pops up, and then disappears.  I can see in the task manager that it is still running, so I guess it is hidden eventually..  but it still opened a window initially.

How do I run a powershell script without a powershell widow opening at all?

Thanks!