If you created a project in controller mode but find that your plugin tracks have no sound in standalone, consider which plugin you used on that track, it may not be compatible with MPC. 
Third-Party VST plugins are not compatible with the MPC operating system, so when your project is opened in Standalone, there will be MIDI data on the grid of that track, but no instrument loaded to play. To hear the notes recorded in the grid, you would need to load a new instrument to that track.

If you wish to use the sound from your original VST, there is a way to do so! 
You can convert the sound from your VST plugin into a Keygroup program and load that Keygroup program onto the track. This tool is called Autosampler. Below is a guide on how to use Autosampler to convert your favorite VST plugin presets into Keygroup programs:

Akai Pro MPC 2 Software | How to Create Keygroup programs using Auto Sampler