Losi desert buggy! Help.....

[xmodsNSX94]

well i got a Desert buggy a while back from a member on here and really enjoyed the time i spent with it, however now ive ran into a problem, i made a video to try and show you as im not that good at describing....


but basically as you increase the accelerator nothing happens, a sounds comes from the motor but the wheels dont move, at all..... the steering works fine however.... the reverse gets no motion at all but the lights on the ESC light up so it receives the signal...

any help is appreciated as to solving the problem...
its a Castle Creations mamba Brushless system installed and im using a 2.4 remote and receiver...

thanks in advance

NSX