Why is my laptop not turning on?

Okay, not that experienced with the 13in unibody but I’ll give it a shot.

1. Try the usual PRAM and SMC reset, I’d especially try resetting the SMC
2. Maybe the display connector has gotten loose? It’s highly unlikely but it doesn’t hurt to check
3. Try booting with the “no battery installed” option. Since you’ve opened up the laptop, you should be able to just disconnect the battery, but try doing the following with the battery first.
   • Unplug everything
   • Hold the power button for at least 10 seconds, don’t release
   • Keep holding the power button, plug in the charger, then hold the power button for another 10 seconds
   • Release the power button, then press the power again like you normally would boot
4. I’ve had to do this for macs without a battery, I think it will also ramp the fans up to 100%, but see if there is a screen.

Dead systems are hard too diagnose. It could be quite a few things which makes tough to fix without following a good diagnostic process.

Wants hard is without having access to spares to slide in and out like a battery, DC-In board & logic board for starters. You then need to test each part discreetly. Referencing schematics and board views of the logic board and using a DVM to measure things.

As you hadn’t spent that much on the system att his point, can you find a second of the same series?