CPU Overheating with fan running at full speed

I'm having a strange issue.

The CPU (Dual-core) is overheating and the computer shuts itself off. However, the fan is running at full speed.

I verified this both using a motherboard monitor and by running the machine with the case off.

It came sort of out of the blue and has me baffled. The only thing that has changed recently is a hard drive replacement, as well as an additional hard drive installed (for backup), however it ran fine for about two weeks after the replacement and for another after the additional hard drive was put in. Power was planned for well in advance, there's plenty to spare and there are plenty of fans, all of which are functioning.

One thought I had, was that the sensor was malfunctioning, I've checked temperature from both the BIOS and from a motherboard monitoring tool that came with the mobo. It says the CPU is running at 180 Fahrenheit (approximately) at a peak. The mobo is running at the same temperature as always.

Any other ideas or thoughts?

If it was the sensor, I have no clue what to do, or where it is.

Mobo is an ASUS P5K.

CPU is an Intel Pentium Dual Core Processor E7300

Sorry about that, I'm Canadian actually, so I would have given you Celsius, but I thought you'd prefer Fahrenheit.

I'm using the stock cooler yes.

The case has been tipped recently yes.

I think you are on to something. I think it might be the pins because I recall it being a pain to get them in to begin with and one not quite wanting to lock in so easy.

I'll have to double check that and then go from there.

I did check it before, but it might have come out when I put it back upright.

OK, so it looks like one of them was out.

The problem is, I can't for the life of me get it back in!

I ended up undoing all of them and they all popped up. Now I can't get any of them back in.

When you turn each one, is the bottom (the part with the clip I'd guess you call it) supposed to turn with it, or is the top independent from the bottom? The bottom doesn't seem to be moving when I turn them.

I put it so the thin edge/notch is outwards like it says too, but they won't for the life of me go back in.

I've read that this system is a pain and have experienced it before (what I wouldn't give for some screws) I'm just wondering if there is a better way, rather than exerting so much force I break my damn mobo.

Well, we found the problem at least lol.

Let's look at one "pin", one corner of the heatsink.

The push button on the top side forces a (black) pin down. When it is fully down, it forces two (white) half-pins outward. These two half-pins have little "hooks" on them that grip the back of the mobo, and prevent the heat sink from being pulled out. To install, you need to get the white pins behind the mobo, then press the black pin down to force them apart.

So the trick now is to raise each black pin UP by rotating/pulling up on the round plate on top (I forget which way lol, its marked with arrows). That will allow the two white half-pins to come back together so you can insert them into the holes. You may have bent the half-pins, squeeze them together so they will fit into the holes in the mobo.

Once each black pin is raised, and each two half-pins will fit in the mobo holes, re-install the heatsink. Make sure you watch the back of the mobo as you insert each leg - that way you will know when the white pins are grabbing the mobo.

(Yes, you must remove the mobo from the case.)

From what I can see, it doesn't seem to be squeezing together (the white pins) at all when I turn it.

edit: I turn it the direction that the mobo instructions state, but I don't see anything happening. I have the arrow/notch lined up as it says to.

As long as the black pin is not down between the two white pins, you should be able to insert them into the holes.

Turn them to the unlocked position and then pull on them.

Remove/Replace the case fan connector. Check for pinching or damage to the wires.

Correlate the fan speed reading with CPUID Hardware Monitor.