Install music recording software, through which you can process your keyboard sounds to turn your PC into a piano. GarageBand is installed by default for Apple users, while Audacity is available as a free alternative for Windows computers.
Open your music recording software application and open the 'Preferences' or 'Options' tab.
Find the audio input/output preferences and select your PC's built-in input as the input sound source. This may be the default option, or you may have to switch from the in-built microphone or some other sound source.
Connect your USB MIDI keyboard to your computer through the USB port, installing any drivers that may be necessary. Most MIDI keyboards are based on 'plug and play' technology, although you may be required to install the application before you can get started.
Activate an audio track within the software and select a piano sound effect for the MIDI input. This will allow you to play and record piano sounds from your computer.