Prime95 fails after 30 seconds!

Hello,
my PC with Win7 is quite unstable, I got many BSOD. I've used memtest86 to check memory errors and it run for 8 hours without reporting problems.
Instead Prime95 v25.9 after no more than 30 seconds fails reporting hardware failure "FATAL ERROR: rounding was 0.5, expected less
than 0.4" on each processor (It's a Core2 QUAD CPU Q8200@2.33 GHz).
I run Prime95 also with Vista and XP on my PC without better luck. Unfortunately I haven't minidump because I have recently installed XP.

My PC shows BSOD even during operating systems installation for Vista and 7. XP seems to be more stable but Prime95 fails to run.

I've always performed a clean installation when I install win7, destroying old partions and building new ones. Win7 behaves strangely.
When I execute disk partitions, it always creates a new partion at the beginning of the disk and one at the end with 0 size. I don't remembet it happened weeks ago...

My PC is under warranty, so I can't open it in order to unplug some boards or change hard disk.

Could you please help me to find a solution in order to have a stable system?

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My SYSTEM:
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Intel Core2 QUAD CPU Q8200@2.33 GHz
RAM: 2x1Gb DDR3
M/B: ASUS P5QC
NVIDIA GeForce 9800GT
Terratec Cinergy HT PCI
Wireless Network Board
Power Supply: 500W (ThermalTake TT1225)

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These are the BIOS Settings:
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Intel Core2 QUAD CPU Q8200@2.33 GHz
FSB Speed: 1333 MHz
Ratio Status: Unlocked (Min:06, Max:07)
Ratio actual value: 7

[CPU Settings]
CPU Ratio Settings: Auto
C1E Support : Enabled

[Ai Tweaker]
Ai Overclock Tuner: Auto
CPU Ratio Settings: Auto
FSB Strap to North Bridge: Auto
DRAM Frequency: Auto
DRAM Timing Control: Auto
1st Information: 9-9-9-24-4-74-8-5
2nd Information: 10-5-7-4-9-4-7
3rd Information: 19-7-1-10-10
DRAM Static Read Control: Auto
DRAM Dynamic Write Control: Auto
DRAM Read Training: Auto
DRAM Write Training: Auto
Mem OC Charger: Auto
Ai Clock Twister: Auto
Ai Transaction Booster: Auto
C/P: A1 A2 | B1 B2
LVL: 08 08 | 08 08

I've change RAM and everything works very well....

Prime95 crashes after 7-8 minutes, but it doesn't matter.... I can use my PC for long time without BSOD!!

Naturally, now I'm using win7. It works very well and it's very nice!!

Степан