Function Get-FileName($initialDirectory)
    {
    [System.Reflection.Assembly]::LoadWithPartialName("System.windows.forms") | Out-Null

    $OpenFileDialog = New-Object System.Windows.Forms.OpenFileDialog
    $OpenFileDialog.initialDirectory = $initialDirectory
    $OpenFileDialog.filter = "PS1 (*.ps1)| *.ps1"
    $OpenFileDialog.ShowDialog((New-Object System.Windows.Forms.Form -Property @{TopMost = $true })) | Out-Null
    $OpenFileDialog.filename
}

    $file = Get-FileName -initialDirectory "C:\Users\USER\PATH\Documents\WindowsPowerShell"

   "&'$file'" | invoke-expression