Diagnosing if it’s the hard drive is easy enough on a Mac Book, you can pull the battery, then unscrew the 3 screws on the metal L shaped panel. The hard drive just pulls out. If it was that, the computer should turn on to a screen with a blinking folder and question mark.

RAM is easy too, just swing the two bars under the L panel. The computer should turn on with the sleep light flashing and a loud beeping noise. That’d mean the logic board still POSTs, or successfully runs the Power On Self Test, this is a good thing; it means that the logic board is probably good and it’s the RAM that’s the problem. In this case, try each RAM module individually in each slot. If one works and another doesn’t, you have bad RAM. If one slot works and another doesn’t it’s a bad logic board. If neither works, it’s not as clear what’s wrong. If you have any other RAM (probably pc-5300 for a MacBook), try using that.

If the computer doesn’t do anything different with no RAM, you can try removing the Airport card, but that will require removing the top case. It’s a posibility but I haven’t seen it too many times in practice.

If the problem still exists after this, it’s probably your logic board.

I do this often, so I left my email address if you want to pick my brain.

Good luck!