Hello. I've had about 2 years of trouble-free use of MBP. All original drives, RAM, etc. Running Snow Leopard 10.6.8. It shipped with 10.6.4 and have updated a couple times. Yesterday, after a few days of not using it the machine wouldn't start, it wouldn't respond to the power button. Fully charged the battery and tried repeatedly. Finally it powered up: chime, grey screen with apple logo and timer (this goes for a pretty long time), blue screen for a split second, then it shuts down. Tried resseting the PRAM and SMC and nothing changed. Started it from the Install DVD and was able to run the Apple Hardware Test. Showed no hardware problems. After that was finished kept getting a message "Are you sure you want to shut down the computer? Shut Down, Restart, Cancel. Clicking cancel gave a couple more minutes before the message came back. Finally the computer just shut itself down unexpectedly. After that it went into a weird cycle where it was restarting itself spontaneously for about an hour, getting just past the grey screen and then restarting. That was pretty scary. Was finally able to eject the dvd and it finally stopped. This morning after waching a youtube tutorial i opened it up and cleaned out the fan, RAM etc with compressed air. The startup is the same, gets just past grey screen then shuts down again. Booting from the Install dvd gets it to the desktop. I was able to go into Energy Saver preferences and uncheck the restart ones. Then it shut down without warning. I am afraid to reinstall Snow Leopard because it could shut down in the middle and screw it up. I have read alot of forums on this last night and tonight.