Take out your speedcontrol does it smell burnt? Open up the case if you can and take a look and see if anything has the tell tale signs of a short....i.e. brown orange color on the plastic compenents. You may have blown a fuse. Sometimes the speedo will work but only barely. It will run at half power, or in my case full power. Speed controls are very delicate. My quantum competition two has had many problems with shorts and etc. Make sure you don't ever cut off your switch. That is what I was doing, and it turned out to be a bad idea.
Oh! Take a look at the circuitboard where you solder your powerwires onto. It may have shorted out across the board.