"I was thinking that if I wanted to record my electric guitar I could unplug the keyboard to laptop connection and just plug my guitar into the laptop line in, but this doesn't seem to work and I'm not sure why."


“The output from most electronic devices in an audio system will be of low impedance in nature, usually 150 Ohms or less. However, the output from many passive devices, such as a high impedance microphone or passive guitar pickup can have much greater output impedance. What's the difference and why is it important to know how to deal with these signals in an audio system?”


http://whirlwindusa.com/support/tech-articles/high-and-low-impedance-signals/