The instruments may not have been installed properly during the initial installation. To fix this, go to the Installer CD > SampleTank 2 SE and copy the "ST2SEInstruments" folder. Paste it in C: > Program Files > IK Mulitimedia > SampleTank2 SE, and choose "Yes" to replace the existing folder. Then, go back into SampleTank in Pro Tools and press the "Relist" button. Your instruments will now appear. Remember to double-click on an instrument name to load it!