Slides depend on battery power. If your battery was down that would explain that problem. Next time connect your tow vehicle and start the motor. That should help.
As for the brakes? Several things could have caused that problem. Break away cable came out, brakes not adjusted properly, brake controller not adjusted properly.
As for proper controller adjustment? In a parking lot accelerate to about 20MPH and using the hand control. Apply the trailer brakes. If the wheels lock up and slide, back off just a bit and try again. The trailer brakes should bring you down to a stop from 20 with no wheel lock.