CPU overheat? Thermal Temperature in BIOS? Serious problem..

Question

My computer:
Athlon 64 3000+ 754 BOXED
MSI K8T Neo FIS2R with latest BIOS
PowerColor Radeon 9600 256MB (passive cooling from retail)
Corsair 512MB PC3200 ValueSelect
Maxtor 160GB SATA (old drive)
Seagate 200GB SATA (new drive)
DVD-burner
CD-ROM
Floppy
TV-card
350W PSU from my In Win case, 15A @ 12V
NEVER OVERCLOCKED
I have found this under Power Settings in BIOS. It's set to 65 degrees but I can't seem to change the temperature. I want to change it because I think that it causes a problem to my computer, here's what happens:
When browsing the net or not running any heavy applications my computer is just fine. But as soon as I start playing for 15-20 minutes, a bluescreen appears and I have to turn the PSU off and on to be able to turn on the computer again. Sometimes the bluescreen is all blank, sometimes IRQL_NOT_EQUAL_OR_LESS, sometimes PAGE_FAULT_IN_NONPAGE_AREA but mostly I get a bluescreen about win32k.sys. I read the manual and changed a power setting in BIOS to On (it will reboot, I had it on Off before) if any power faults are detected. So now when I changed that, I don't get any bluescreens, instead my computer freezes and I have to turn the PSU off, so I guess it's all about some sort of power problem. A more indepth description of what happens: After the bluescreen/freeze, the computer is still on and all fans are spinning. If I try to reboot using the restart button, the screen goes black but nothing happens. No beep from the motherboard, and the monitor light just flashing, but the fans are still on. So I turn off the PSU power on the back of the PSU and then turn it on again. If I try to start the computer too fast after turning the PSU off, the computer will most likely freeze when NO BIOS FOUND appears or the Windows XP Welcome screen appears. And if I then try to reboot the computer keeps freezing before Windows is loaded, and sometimes it will not even start (no beep, monitor all black). So I have to wait 5-10 minutes before I turn the computer on, and I have no idea why. It's always running fine if I wait. And the problem doesn't just occur when playing, but when having Prime95 on as well. 5-10 minutes on torture test then bluescreen.
My problem appeared when I installed a new harddrive. My computer has been running fine for over 1 year now, but after installing the new harddrive and Windows XP on it (removing Windows on the old hd as well), it's all weird.
Now this is what I have done so far (it's a lot):
-Installed a lot of different drivers and updates for the motherboard and the graphicscard.
-Installed another version of Windows XP.
-Formatted the new harddrive and reinstalled Windows XP ~5 times.
-After installing XP, the first thing I did was to run the game, without ANY drivers at all. This made me think it has to be a hardware problem, since I still got a bluescreen.
-Updated BIOS to the latest, because I read some temperature problems were fixed. Actually the update lowered my CPU temperature by ~15 degrees but still bluescreen.
-Ran the computer with an open case for better airflow, unplugged the old harddrive + DVD + CD + floppy, running with only CPU + RAM + graphicscard + hd, to see if there was any power problem with my PSU. But as the bluescreen still appeared, I bet it wasn't any power problem (plus the fact that my computer has been running fine for 1+ years...)
-Changed my memory to 2x Kingston HyperX and disabled External BIOS Cache + Shadowing in BIOS, with no effect. So I suppose no memory problem..
-Read about the NONPAGE bluescreen that it can occur if the harddrive is trying to read something that does not excist, or something like that. Not really sure what it meant, but I started to think that the new hd was the cause of the problem.
-Ran Scandisc on all drives.
-Moved the game to my old drive and ran it, still same problem.
-The last thing I tried to do was to install Windows on my old harddrive, exactly like it was before, but I got a bluescreen under the installation and was to tired to try another time.
So... my conclusion is (but it might not be right though):
Either
-Harddrive problem (bad sectors?)
-CPU overheat problem (rebooting/bluescreen because of too high temperature?)
-Graphicscard problem (overheat? no idea...)
Alright, this is as much as I can do. I've been to various forums but I haven't got much help. I hope you might know or give me some ideas of what is wrong! :/

Answer 1

I set them to the correct values. Underclocked. Doesn't help. Tried 3 different DDR modules, didn't help. Tried to switch memory slots, didn't help.
On the memtest86 website I read that it could be either memory, CPU or motherboard problem if the test fails. So I guess either CPU or motherboard. I still think the CPU is overheating, because when I looked in BIOS the idle temperature rose to 70+ degrees. Could be bad sensors, but I got the latest BIOS. Everytime I try to install Windows XP I get a bluescreen, and my computer even froze in DOS-mode. I might think it's hotter where the temp sensors are than the actual CPU temperature, so they give false values. Or maybe my CPU is just too hot, I don't know. And that's maybe the cause to why I get millions of errors in memtest after a while, because the CPU gets too hot.
What do you think?