Iphone 3g vibrate only and lcd won't turn on?

Already try with other lcd but same result. Need help

You probably cut or ripped your display (LCD) panel cable. For this problem you would have to get a new display (iFixit Part No. IF137-001-1). You can make sure that the device actually works by turning the vibrator switch on and off and if you feel any vibration, then the display is the problem, not the phone itself.