Guitar Pro opens correctly and you can hear the introduction jingle during the opening but no sound comes out from the program when you play a file.
Once Guitar Pro has been correctly installed on your computer you still need to download and install the last available updates and soundbanks.
Steps for Windows and Linux:
Launch the Updater from the "Help" pane and install any available updates.
Steps for Mac OS X:
Launch the Updater from the "Guitar Pro" pane and install any available updates.