Here's a game idea generator. http://orteil.dashnet.org/gamegen

But if you're new and are just learning gamemaker (I'm just making assumptions here, so correct me if i'm wrong), I would recommend going through the gamemaker tutorials. They have you make some simple stuff like a top down air plane shooter, and brick breaking game. As you learn the types of things you can do from the tutorials, you can think about what type of games you can make within your current limitations. Working within limitations are a great way to come up with creative ideas, and by limiting your game to what you know how to do, you're more likely to complete it.