Last week, it was experiencing the dreaded random shutdown disease. Thinking it may be a memory issue, I swapped the 3rd party RAM back to the original sticks, but that didnt cure it. It was fine for about a week, so I thought I would put the 3rd party RAM back in, and everything would be alright. When I did, it didnt want to start up. The optic drive was constantly stopping and starting. After a few attemps at starting in several circumstances (battery out power in, power out battery in, PMU reset, then repeat) it finally made the normal noise, but no Sosumi (the startup bong noise) and nothing on the screen. The light next to the IR receiver turns on, and stays on. It seems my beloved is in a coma! Its going back to the AppleCentre, maybe for a heart transplant (logic board replacement). Point of this thread; if you are having the random shutdown problems, back your HDD up, and take it back. Better to return a sick MacBook than a departed one.