Intermittent / sudden cessation of service

[Telegram_Sam]

According to my Account info I am using Spotify Free on my desktop PC, and this has satisfied my modest requirements admirably in the past - I use the web player (Chrome + Windows 7). Now it appears sometimes to work, other times not to play anything at all, and at other times to start working (through for example my playlist) and then suddenly go on strike.  At such times the track title "Advertisement" appears at the bottom of my screen, but no sound.

I have not downloaded the App mainly because I don't know what it does and because I have been able to survive OK in the past without it (if it ain't broke ..)

Can someone kindly tell me what is going on and how to get back to the previous state?  Thanks.