The PowerShell script doesn't launch PS1 file.
It has field "Script Body", where you should paste your script.
There is example how to create PowerShell monitor: http://www.solarwinds.com/documentation/en/flarehelp/sam/content/orionapmagcreatingpowershellmonitor.htm
In step #12 you place text of your script.
The script should end with cmdlet to pass statistic value to Orion like this:
Write-Host 'Statistic: ' $MyValue
exit(0)