"Line in" on Acer Aspire Laptop

I have a Casio Celviano Digital Piano (AP500) and want to record from it onto my laptop.
I tried recording with the inbuilt microphone on the Laptop but the sound quality was totally unacceptable.
On the Laptop I switched audio inputs from the microphone to the stereo mix.
I downloaded the relevant USB MIDI driver from Casio and installed it, but cannot get a connection to the laptop.
I have tried to directly connect from the Line Out of the piano to the Line In on the laptop and cannot get a connection.
Obviously, I'm doing something wrong - can anyone help, please