apk files usually aren't disabled, it's the apps that the apk file installed that get disabled. An apk file is just a zip file with different letters in the extension (open one in a zip program and you'll see) that's used to install an app by the installer. ("Sideloading" just bypasses the play store - which can be dangerous - it doesn't turn an apk file into an app.)
Bibz, if you don't have every single one of those songs backed up on another device (cloud accounts count as devices), you're doing it wrong. One truck riding over your dropped phone and you've lost thousands of songs. If they're backed up, you can reset, then reload them.