The virtual instruments are installed form a separate download available in your Avid account.
Log into your Avid account here.
Go to Your Products and expand the Downloads links.
If you have Pro Tools 11, download and install the AIR Creative Collection.
If you have Pro Tools 10, download and install the Avid Virtual Instruments
If you have Pro Tools Express, download and install the Avid Virtual Instruments Express.
Be sure to choose the correct installer for your computer’s operating system.