Ah, there you go. Cubase allows just 1 driver to be loaded at a time. That means if you load your Yamaha driver, Cubase only sees the in and outputs on your keyboard. Your laptop in and outputs will be unavailable.
There are 2 options for you. The first and best is to connect your speakers to your keyboard outputs instead of your laptop output. This is better because the yamaha ASIO driver is much better than the generic ASIO driver you will need for your laptop soundcard. If you are saying you are using the actual built in speakers on your laptop (boooo!), then this is not possible of course.
The 2nd option is using a driver to use with your onboard soundcard. There is usually some Generic driver available in the VST audio system tab that will work, but they often have huge latency and quickly start dropping out when under load. If you experience problems like this, you can try ASIO4all instead, that’s a better performing generic ASIO driver.