Re: how do I download my play store music on my PC
Welcome to Android Central! If you have All Access, I don't think you can download any old song from the vast library to your computer--that would enable a lot of people to start sharing lots and lots of music illegally with others. You can download to your PC any music you uploaded yourself (i.e., mp3's you ripped from a CD) or any music you bought separate from All Access.
You can temporarily download a song from All Access to a device (phone or tablet) using the Google Play Music app, but that music track is stored in a hidden directory with a coded filename, so you can't transfer it or otherwise manipulate it.