I had a problem with spotify not playing most songs (they didn't show info and bar didn't move) so I reinstalled the program. Now it doesn't play anything and claims all my playlists are empty. This is only on pc, my phone app works totally like it should.
Make sure to open "hosts" and not "hosts.txt", because the latter one is in fact not being used by the system and is just an example of a host file. (you might want to turn on the file extensions and also make the browser show hidden files; you can search for it on the web)
2) Remove all lines containing the word "spotify" in them.
3) Save the file. (you will need admin rights)
4) Spotify will sync with your other online devices and will be able to play music right away. Even without a restart.