Today I found my MacBook in strange state - battery almost fully depleted, very dim display (almost black) and unresponsive. I had to depress the power button for 5s to switch it off. Problem is, even after recharging the battery, it will no longer boot: it hangs when the screen gets grey, after the boot sound but before the Apple logo. I tried resetting the PMU and the SMC, tried booting in safe mode, but never got past the grey screen. I checked my HD in another Mac - it is ok -. I swapped my SIMMs and even tried booting on a single one. Anything else I could try???