Since you are new to riding and the GS I'll advise you to make sure you remove your foot from the shifter completely before trying to down shift to each lower gear. That ensures the ratchet mechanism is released. If you are still holding it (even a tiny bit) after the shift it will not go any where no mater how hard you try. Ever see a video of automobile drivers that thought they were hitting the brake pedal but the foot was on the gas pedal instead? No matter how hard they press the foot (brake) the car accelerates! If that does not help then try some of the other suggestions offered here.
2009 R1200GS (Gone)