First off, have you already attached your account to the Play Music app on this phone? That has to happen first. You have to open the app and go through the initial setup. I screwed it up the first time. I tried to input my gmail and password, but was told the account was already attached to the device, which is fine, but then I had to select the account and it completed the setup. If you have done that the next step is: Settings > Accounts & Sync > Google > Sync Google Play Music.