Try to reseat the ram and do a SMC reset. If it doesn't work:
Take off the MB top case, disconnect the optical drive, the airport card, the hard drive, the battery, from the logic board. Install your hard drive in an external USB 2.5 enclosure and connect it to the USB port, connect an external keyboard to the MacBook, find the two small power pads on the logic board (it's near the fan and you'll see the power icon over them), connect the AC adapter (diode should be green) and trip the two power pads with a small flat jeweler screwdriver. If you get a chime push on the keyboard option key and you should see the external HD icon onscreen. We want to know if the logic board has a problem or if something else is causing the issue. If the MacBook boots than you have a bad cable or bad top case or another faulty part that you'll have to find. If the MB doesn't boot then something else is in trouble or the logic board is dead.