Active games in which your opponent has not moved within a certain number of days are not shown on your game status page. This prevents the page from becoming cluttered with idle games.
You can set the number of days after which an idle game disappears from your game status page. Click 'My profile' in the left-side menu column. On the profile page, adjust the setting 'Don't show games idle for more than __ days.' The default is 14. Whenever you change something on the profile page, be sure to scroll down and click 'Submit.'
If an active game has disappeared from your Game Status page, it still remains on your opponent's Game Status page to remind her to move. If she takes her turn, the game reappears on your Game Status page in the list of games in which it's your turn to move.
Games in which it is your turn to move never disappear from your game status page. If you do not wish to play one of your games anymore, please resign from that game so that your opponent does not wonder what happened to you.