get-openfiles with- not recognized as the name of a cmdlet

Hi

I used able to run this script below, no idea after restart my PC and now i get error "get-openfiles : The term 'get-openfiles' is not recognized as the name of a cmdlet, function, script file, or operable program. Check the spelling of the
name, or if a path was included, verify that the path is correct and try again.", Anyone can advice me.

Thank you.

get-openfiles -computername hostname | ? {$_.itempath -like "*.pst*"} | Out-File "$logPath\$computers-OpenFile.txt"