Why are my playlists no longer working?

I tried updating iTunes to the latest version but still no luck. When I play a song on the playlist, instead of going to the next song when the first one ends, it will just stop playing music (kind of like when you reach the end of a CD). It's kind of annoying having to individually select each song I want to play, when I have them all in a playlist. I have tried both using playlists I had previously created (that used to work) and making no playlists, and both have not worked. Any ideas?