Also, check your crimps on your battery connector. This is probably the most mechanically stressed connection in most people's machines as it is the only one which gets moved every time a battery is changed. Also, it is the highest electrical load connection in your robot. I suggest checking both your ground and positive terminals going into your distribuition and breaker blocks respectively.
Our positive terminal came off of our robot at the end of our first semifinal match in Chicago... thankfully we noticed it when it fell out of the robot while changing the battery!
Then again, we also had the eh.. small problem... of one of our ultrasonic sensors catching fire... but that's
another story entirely.
Hope you find your problem! If all else fails, tug on wires and see what pulls out/moves easily.
-q