Well IMO the heatsink is likely to "fail"; it's mostly a block of metal, so if it's visually undamaged and the fan spins at an appropriate speed, then it's probably fine.
CPU is simply an unlikely problem, though we haven't ruled out that possibility.
That leaves thermal compound/user error in applying it, which is probably the trickiest part.
Other than that, I really don't know as case flow/ambient temperatures have to be on the extreme spectrum, I would think, to cause such high temperatures.
If the OP knows if this was a sudden occurring, or a gradual buildup, that might shed some light.

idk i dont think the ambient temp is the problem.. although since u mentioned about video card.. its made me think.. I recently replaced the video card.. I had an older gt260 or something like that,, and now i put a gtx275..im just trying to remmeber if the problem started before or after i put a new graphics card.. but still, i dont think the card makes so much heat to make the cpu overheat that much..

the problem wasnt a sudden occuring.. It started shutting off like once or twice a day.. but i still continued working on it.. and i even used Vegas Pro to edit videos, and it published my videos fine. then with every few days it got worse, started shutting off randomly while i was editting videos.. and then soon i couldnt even publish my video cuz of it shutting down every single time..

the heatsink seems to be working properly.. it spins at regular rate, and its overall physical condition is great too.. (although.. when i took it off, i saw that like one of these, metal things.. however they are called.. the silver lil small plates under the fan, one or two of them were a little bent at a corner, but i dont think that has any effect at all.. and i really have no idea HOW they got bent.. its like.. the corner of it, was bent on 90 degrees to the side.. and i couldnt even straighten it out with my hand)

abient temp.. maybe that is the problem.. the weather got a lot better here in sacramento.. and now its actually a little hot in the day.. + my door is sometimes closed and it gets a little hot in my room.. however,. i got another comp, tower, standing a foot away from this one.. and when I use my other one.. it works great and temp of cpu is around 40-50C which is fine.. (its an Intel core2duo 3.17ghz though)

thermal compound.. umm.. i admit this is like only my second time in life applying it.. but i didnt think its really that hard.. i put a little of the compound, spread it evenly, covered the metal part.. and it was a thin layer..

Looks pretty decent actually...
I also do not think that the ambient temperatures are the problem, even in Sacramento.
I didn't say that thermal compound is the problem, per se, it's just really the only part you can screw up on.
Since it sounds like a general degradation...actually I have no idea what that means. It could be that the thermal compound was very poor and dried out, but that's a total guess. Again we also might want to consider that the CPU itself has a problem, or maybe the motherboard is overvolting due to a malfunction. If you could swap parts around with another computer...but I know that's a hassle.
Maybe someone else knows what's going on.

water cool it :slurp:

I had a similar problem with one of my older rigs. I cleaned everything, put on a V8 cooler (on an Athlon 64), even turned a desk fan onto it on full blast. Nothing helped. So as HK said, its probably motherboard or CPU. I ended up replacing my CPU and board, but if OP has some spare parts he can pop in, he might be able to isolate the problem.

I would recommend taking a look at the 6 core AMD chips (or Intel if one is rich), if his video editing software takes advantage of the multi core setup, he may end up getting better performance.

Another suggestion would be to install some kind of CPU throttling software, and see if the problem persists if he caps it at some percentage.

But I think if you eliminate all the common problems, the most likely one is that the hardware has just reached the end of its life cycle.

There are still a few things I would try to at least isolate the underlying problem. Seems to me that it's one of three things:

1. The motherboard is overvolting the processor.
2. Not getting good contact between the cpu plate and cooler or maybe bad TIM application.
3. Outright cpu failure.

Still think it would be a good idea to disable Turbo Boost and Hyperthreading, would also manually set vCore instead of running it on auto. Would try a few different vCore settings and monitor to see how closely the changes are reflected.

Probably a good idea to check the cpu plate to make sure the surface is even and not warped, same for the cooler. Might also be a good idea to make sure the bios is current, if so ... it still wouldn't hurt to load default settings and then make the above changes.

ok ima try doing some of the proposals here, ill be back when ill find something.. thanks for the help everyone..

I have had a similar experience before. I was running at 70c idle and about 90-100c when gaming etc.

The problem was due to my heatsink and I replaced with an Arctic cooling heatsink (and fan... why not). The idle temp dropped to 40c so double check there are no cracks etc on the heatsink that are preventing the heat from being drawn out.

Sounds like the heatsink is not clipped on properly or there is something like the plastic protector on. The stock heatsinks on Intel chips since the Core 2's have given great stock temps from my experience.

On my i7-920 under load I'm getting 52C. Ambient is probably around 20C atm.