I have a 17inch MacBook pro 2.6hz Penryn model. I've tried searching the forum to find out my problem but i couldn't find anything. it shuts down immediately as soon as i turn it on, this of course after long term use. I thought it was the heat-sink so I re-applied the thermal paste with one from a electronic store. For about two-weeks or so everything was fine now my problem has started again. To give you an insight to what happens to my Macbook, I've found a YouTube page of what happens. This is what exactly happens. It NEVER! shuts down when it's on, only when i restart it, it shuts down immediately, then i have to let it cool down. Then it works again Can anyone tell me what you might think the problem is or point me in the right direction?