As someone else has already explained, it is likely that you have problems with the mating surfaces of the heat sink and cpu chip.
The first thing to do is double check that the Heat Sink you have is rated for your CPU.
If it is, take off the heat sink and clean it thorougly with rubbing alcohol, make sure there is no thermal compound anywhere on the sink. Also make sure you do not have a pre-aplied thermal interface on that heat sink, if it's there it will look either like a small square of foil with a black material underneath or a patch of rubbery stuff. Remove that also.
Now take the CPU out of the socket and clean it with alcohol and a q tip... get all the heat sink grease off it as well.
Both CPU and HSF should be cleaner than new. Both should be bare metal surfaces, at this point.
Now put a small spot of heat sink grease about the size of a match head on the cpu. Tap it out across the entire top metal surface of the cpu. It really doesn't matter which heat sink grease you use. What matters is that you have a <b>very thin and even layer</b> across the entire heat transfer plate of the cpu. More is not better.
Next put the CPU back into it's socket and make sure that when you close the ZIF lock, the CPU is sitting flat against the socket... this is very important to getting a good contact with the heat sink.
Now, put the heatsink back on... If it has a step on the bottom be sure the high part of the step is over the cam box of the ZIF socket. Backwards spells disaster.
Do up the clips for the heat sink and give it a very gentle rotary twist back and forth with your hand. Don't force it, just make sure it's well seated and locked into place.
If you would like illustrated instructions on how to apply heat sink grease, you can find them here: <A HREF="
http://www.arcticsilver.com/arctic_silver_instructions...." target="_new">
http://www.arcticsilver.com/arctic_silver_instructions....;/A>
Finally, when you restart your computer, immediately jump into the BIOS and be sure the frequencies and voltages are set right for your particular chip. Over voltage == more heat. Overclocking == even more heat.
And as has already been suggested, you probably do need to significantly increase the airflow through your case. At least ad an exhaust fan on the back.
Your final temps should be in the high 30s or low 40s.
<b>(</b>It ain't better if it don't work.<b>)</b>