Enormously scary thermals

About a year ago, I had built a monster computer with the interest of doing heavy duty video editing and gaming. My cpu is the intel i7-975 extreme with the stock cooler. Just recently, I have noticed my core temperature spiking to the point of causing me to break out into a cold sweat. 100 Celsius, then it begins to throttle down.
Idle temps are fine - 40 Celsius range. But as soon as any sort of light load is introduced, the temperature spikes to 72 Celsius and steadily rises to 86. If I run a full load cpu stress test with p95, it immediately jumps to 100 Celsius then begins throttling down.
This is only a recent occurrence however. When I first installed the cpu and cooler (cleaned with arcticlean, then topped with ceramique) the idle temps were 32 Celsius, and 55 under maximum load(stock). When OC'ed to 4.2 ghz, temps were 66 under load, and I don't remember the idle temperature. The cooler has never been taken off since the installation.

Does anybody have any ideas? I want to think that it is the thermal paste... But I have never heard of ceramique going bad within a year. Installation of the stock cooler was a bit finicky with getting the pins to go in right. Could it be that one of the plastic pins broke off at some point, for some reason, and is now allowing air into the cpu/thermal paste/cooler interface?

And just to note: the only reason that I haven't torn apart the computer looking for physical reasons behind the problem is because it is my fathers computer. I am 16, and have built and maintained it for him because it cannot find the time required to assemble the computer, install the software, tune it, and so on... Essentially what I am saying is that I would like your guys advice on where to begin, and my father wants a second opinion as well.

Your current temps(62c under load for 4.2GHz speed) is fine, maybe the first time you didn't apply enough thermal paste, and therefore you got significantly high temperatures.

Those temps are my old ones. I have never touched the cooler or anything since the first installation. It is only recently that it began to spike un-provoked. I never touched it, and all of a sudden -- the thermals are going whacko

I'd just reseat it. The most likely problems would all be solved by doing so. If you're still having problems after that, then we can go from there.