Here's the first test:
Remove the battery too. Remove all cables (i.e., speakers, front LED, microphone, keyboard, subwoofer, airport express, et al). Then, connect the HDD and the display. So you'll have nothing but the logic board, RAM, HDD and display. Connect the power adapter. The light should glow green.
If the light on the MagSafe doesn't glow, the adapter or the Logic Board is the issue.
If it works, use something small, metallic and flat-surfaced to jump the power button on the board (I used the end of a screw-driver bit). The jumper is two small solder spots right above the keyboard port.
If it doesn't boot, then it might be the Logic Board, RAM or power adapter, though Logic Board is the best bet.
Shut it down and attach a keyboard (not internal keyboard). Start up again and hold alt. If the boot partition is displayed, then yay! If not, then either the Logic Board is the issue, or you need to reformat the HDD and reinstall the OS.
You can keep adding peripheral one by one and see what screws it up.
I hope this helps.
Regards
Raptor