I'm not aware of all the situations that can bring about a thermal shutdown, I'm just commenting on heat sinks because I've worked with my own recently. My understanding is that it rarely happens unless your computer is overclocked and unstable, though the newer i7's run hot with the stock heat sink. Do you have a program to check your CPU temperature(s), like RealTemp? If so, you can see how hot it is running during various tasks, idle, gaming, folding, what have you. Then, if you still feel the need to try working with the heat sink, you could try applying new thermal grease and re-seating the heat sink, afterwards comparing your temperature readings with those before the work done. If it still doesn't drop, perhaps a 3rd party heat sink would be an option.