Have you managed to connect to the game? In the network settings, the lower section of the page should have a "Connect" button, as well as show if your connection was successful or an error. If you're not getting connected to the server, it won't prompt you to log in either.

It could also be a firewall issue and you'll have to enable The Endless Forest in your network settings. It'll appear as "forest" in the list of available network connections. Running the game in a window with minimal graphic settings can also help as well. There isn't anything wrong with the copy, the game is just old haha and can be a bit harder to deal with in terms of connecting to the game.