a. Display cable If the display cable works loose from the logic board, the video display will not appear. The solution here is to have an Apple Service Provider reconnect the cable and add a foam gasket to the underside of the brightness and speaker grill (service part number 875-0283). The gasket prevents a future disconnection.
b. Battery On a few 3400s, the battery does not maintain contact well and may become disconnected while moving the 3400, resulting in a loss of power when running on battery (an issue previously mentioned here). To solve this, a foam gasket should be added to the inside of the battery bay. The gasket is user-installable and is available free. Call 1-888-273-3594 and ask for service part number 076-0706.