سلام
مشكل شما ربطي به Environ و اين چيزها نداره
شما داري سعي ميكني يك فايل رو با explorer اجرا كني و اين برای همه فایلها ممكن نیست، بايد از تابع ShellExecute استفاده كني
Private Declare Function ShellExecute Lib "shell32.dll" Alias "ShellExecuteA" (ByVal hwnd As Long, ByVal lpOperation As String, ByVal lpFile As String, ByVal lpParameters As String, ByVal lpDirectory As String, ByVal nShowCmd As Long) As Long
Private Sub Form_Load()
ShellExecute Me.hwnd, "open", "h:\Temp\ahang.mp3", "", "", 3
End Sub