Message for Solara

I have a Speed Passion Reventon S which I had loads of problems with when I first bought it, but quite like it now (apart from an intermittent problem with the reverse !). I bought another in a package from RCMart and in its first race the speed controller broke down. I've reloaded the firmware and re-set up the ESC but apart from an initial burst of power, the car slows right down to a stand still and doesn't go again. Any idea what the problem could be ? It's really affecting my confidence in Speed Passion products.