I just finished building my first computer. When i boot it up all goes well, as far as configuring the bios; but i can never get very far, as the computer shuts its self off anywhere from 45 seconds to 3 minutes after I turn it on. The CPU led turns red, and when I try and reboot it I get a beep code signaling the CPU just overheated. I do not have a device for measuring the temperature, but I can say it certainly does feel warm. I use the heatsink that came with the quad core, could it be that the heatsink needs to be upgraded? Or does the fact that it overheats so quickly indicate something far more difficult. When this first occured repeatedly i disassembled and reassembled everything, double checking everything to make shure it was installed properly; also, im positive the heatsink is making full contact, and that there is adequate compund between the cpu and heatsink.
Please Help. Thank you.

If you can get into the BIOS, you should be able to stay there long enough to use the BIOS health monitor to see exactly how hot the CPU is getting and how quickly it is getting there. Also, if you have removed the heatsink, you will need to clean it and the CPU heat spreader and reapply fresh thermal grease, see here:

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This is unlikely... but if you can get into the Bios Menus see if there is some setting that makes the computer reboot at a certin temp.
If its set that 40C is to hot and the CPU idles at 41C or higher that might be your problem.

Thats all I can think of..

Is the fan even running? You don't even mention whether the fan on the heatsink runs.

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