Switch wiring reversed? If the reverse gear is engaged when in overdrive, major damage is likely to happen. It may already have happened unfortunately. Make sure that the oil level is good.
With engine not running, put it in top gear and switch the ignition on. Switch overdrive on and listen for the solenoid to "clunk" If it's a quiet environment the noise should be obvious. If noisy you might have to get out and listen under the car. Better still have someone hold the solenoid while you switch the OD on and off.