I've just been given a 2007/8 model, which, although previously working before being shelved for some (unknown, perhaps lengthy) time won't boot. On pressing the power button there's a whirr (fan?) and what I think is the 'click' of the optical drive, and a second-or-two later it's all quiet again (without a chime). It's plugged-in and the battery is charged. Same thing when trying to option-boot to external usb. I've reset SMC.