Yesterday, my dad's older Macbook Pro was on the fritz (graphics issues), so he switched to using his newer one. He set the newer one on top of the old one, and it resisted to boot up, even when we could see the status light on it, and we heard the drive spinning. For giggles, I told him to lift the new one off the old one, and whazam, the login screen appeared. Is this a coincidence, or is there deeper magic at play?
It sounds like their magnetic latches are interfering with each other. See Apple's support note: Mac notebooks: Magnets in devices may cause computer to sleep unexpectedly