I think I have figured out the problem...

I've been posting a lot here about my CPU temperatures, and now I think I have figured out what's wrong. I'm almost certain now that either the temp sensor is bad, or that SpeedFan, SensorsView, Everest, and the utility that came with my mobo, are all reading the temperatures wrong.
I just reimaged my computer with a fresh hard drive and round IDE cables and SATA instead of IDE for the hard drives. More airflow, less heat. First time when I started up Windows, SpeedFan and my others were giving me around the same reading, about 28-30°C. while idling. I thought that maybe it was because I moved my computer off of the floor and up on top of my desk. I was not seeing temperatures above 40. I thought it was fantastic. THEN, when I left out of the room to go get something, left the computer running, I came back in and the computer was off. It turned itself off. When I rebooted, I went into the BIOS and checked the temperature, it was all good. When I started windows, I noticed that my idle temperatures went up by 10 degrees. Now Idling at about 38-40. I tried restarting, reinstalling the software, tried turning it off and letting it sit, nothing seems to matter.

Also, while I was writing this, I noticed that my temperatures were all over the place. All I have open, right now, is one instance of Internet Explorer, and that's it. My temps were going up to 54-56, then coming back down to 23 in a matter of several seconds. This has to be a bad temperature sensor, right? I mean...why else would the temperatures be spiking like that. Is it even POSSIBLE for them to change from 56 to 24 in only two seconds?

Thanks