Hi there Alfonse, welcome aboard.
Have you installed Guitar Rig 3 yet?
If so, have you launched it in standalone mode (by default it installs to
Program Files > Native Instruments > Guitar Rig 3) and registered it yet? Registering the product will change it from the
Demo version to the
LE version.
If not, I believe it's recommended that you do this before using the VST plug-in version inside Guitar Tracks.
I can walk you through using it in GTPro4 once you have it running on its own.
Steve