The game is listed with the following system requirements in order to run properly:
Internet: Internet Connection Required
Operating System: Windows XP or newer versions
DirectX: 9.0c or newer
Processor: 1GHz Intel Processor
RAM Space: 512 Megabytes
Video Card: Best results with GeForce 2 or equivalent (standard in most PCs)
Disk Space: 5 Gigabytes
Game Download: The game automatically initiates a download in the background when you log in to play for the first time. The process is transparent to the player. No special installation process is required. You must, however, be connected to the internet.
Make sure you meet these requirements and the game will work properly. Alternatively, try to re-install the game.