This sounds like a graphics problem. When you load the game (assuming that it's only when you play a game and not load it that it'll freeze) log-in and in the top right hand corner there is a picture of a Cog, click that. It will open up a dialogue box and you need to select graphics, then set them to "low". You can gradually move your way up to better graphics, but doing this will let us know if it's a graphics problem that can be easily fixed.