Yeah... good advice. Know your socket. At least it sounds like good advice, until you realize there like a gazillion coolers out there, all that will work on your socket. Hell, without trying to shop FOR you, I can tell you that THIS is your processor, and it is socket LGA775. Heck, you could use the after market cooler I'm using with my AMD Phenom II x6 T1100... since it is a great cooler, and it works with a multitude of sockets. But, then I'm recommending a product, and that is approaching the whole shopping prohibition.
You are afraid that your computer is shutting down due to overheating. Well, first of all, the stock heat sink and fan that comes with a processor when you buy the retail package is nothing to get psyched about, but it is more than adequate to cool the CPU.
So, as has kind of been pointed out to you already, you need to actually examine what your temperatures are. Which means your question should really be...
How do I find out if I need a new heat sink?
First, you start with a program like Speedfan. You see what your temperatures are currently at. Then, if you are actually overheating, you take a close look at your existing heat sink and how it is mounted. For all you know, it might not be seated properly on the processor. There might not be an even, thin layer of thermal paste between the processor and the heat sink. The fan might not be spinning properly, or mounted on the heat sink right. There might even be a ton of dust within the heat sink that is keeping the air from flowing through it.
So, more important than posting the specs for your video card, you should be posting your current temps. Pics of your heat sink. Pics of what your processor looks like immediately after pulling your heat sink off.