Thank you for your replies.
Did you create your device with the D3D11_CREATE_DEVICE_DEBUG flag enabled? If you do that, you'll get error messages in the debugger output telling you why API calls failed.
I create the device without that flag, I'll try to put it in and see if there will be error messages.
The geometry shader is compiling, but the "CreateGeometryShaderWithStreamOutput" call will give me a null geometryShader value.
This is an indicator that your GS code is valid but the actual GS bytecode created by compilation won't run on your hardware (compilation doesn't do hardware validation, creation does). I see that you're compiling with "gs_5_0" so the first thing you should check is that your hardware actually supports shader model 5.
I'm running the program with a geforce gtx 860m, which fully supports shaders v. 5!
Which feature level did you create your device with? Even if your hardware is capable, you can easily request a lower feature level and cap yourself regarding shader level!