My Prime95 always Halt when FFT size is 16K

Hi all,
My Prime95 always halt execution when FFT size reach 16K,
message like this :
[Fri Aug 06 07:49:33 2004]
FATAL ERROR: Rounding was 0.4990921021, expected less than 0.4
Hardware failure detected, consult stress.txt file.
and if I use custom test with a 18K FFT, after about 10 seconds the computer will no response any more, so I had to press "Reset" or shutdown it.
It happens every time.
my pc's spec: Abit NF7-S2(Nforce2 ultra 400 spp+Raid MCP), athlon 1800+ (palomino 0.18), Kingston DDR 266 512MB * 2 in Dual channel, Inno3D 5900XT 128MB. I didn't overclock anything.
I have used memtest86 to test my RAM 1 pass with no error.
and Sometimes my PC will randomly reboot( I suppose this is a bluescreen error, but I have set automatically restart so I didn't got the error message. )
I want to test it again with the boot disk with mprime this night.
any idea will be very appreciate

[eydolic]

I would download a good readout utility such as MBM5 and make sure that none of your voltages dip severely as you get closer to the 16K mark. If the voltages are unacceptable (some can be adjusted to be within spec) then you will probably need a new PSU. You might up the vcore a notch just to make sure that the processor is getting enough power, and of course keep an eye on the temperatures since Prime95 keeps your processor usage at a constant 100%. If your memory passes Memtest86+'s complete test then you might try looser timings or a higher vdimm to see if Prime95 has an issue that Memtest86+ doesn't detect.