I just bought and installed an i5-2500k. I was going to overclock it a little, maybe to 3.7GHz, but when I got into my bios it shows my CPU temp and it was showing 97 degrees Celsius for CPU temp. I don't know a ton about cpu's, but I do know that's HOT. I shutdown, re-installed the CPU and heatsink, then booted up again to see that it climbed extremely fast to around 90 degrees Celsius, and then eventually up to 97 again.
Any idea what's going on here?
Btw, I checked the temp with a program to be sure I was reading everything right and it actually reported higher than my bios did.
The reason it's cooler in Windows than in the BIOS is that the power saving features aren't active in the BIOS and there is actually a small load on the CPU in the BIOS. In Windows, the power saving features (SpeedStep, etc.) allow the CPU to idle at a much lower speed and voltage, so that's why it's cooler.
As far as your problem goes, I assume that you're using the stock cooler, correct? Well, the thing about the stock Intel coolers is that you can think that it's absolutely secure, but not actually be.
The pins are actually quite difficult to get properly seated, and if even one isn't seated properly, it'll cause what you're describing.
Also, the fact that you re-seated it (if you took it completely off), and didn't clean off the old thermal paste and reapply new paste, doesn't help, either. You always need to reapply new paste if you re-seat.
The thing that you definitely need to do though, is check to make sure that all 4 pins are properly seated and pushed all the way through to the back of the board. You may even need to take the board out to confirm. It's seriously that difficult to get right (especially if you've never done it before).
I would seriously like to have a nice long talk with whoever though that the pins were a good idea because they aren't, lol.
Edit: amuffin's guide shows exactly what I'm talking about.