Click on the quarter note button to access the options. Click on the Pattern tab and turn on all of the stings.
Make sure if you are using a song with "Auto Select" as the default pattern that you change it to a specific pattern as the "Auto Select" will turn off the strings like you are experiencing. Example: Bebop Major Jame has "Auto Select" as its default pattern. Click on the "P" button to change it to "Major" and it will not turn off the strings.