Random Power Off and Reset

So, I have an Athlon 300+Mobile running at 133*14 (1866), 512MB PC3200 running at DDR266 (133 bus speed to sync w/processor), and a 9600Pro AGP video card. My PSU is a PowMax LP-9900 400W. I have 1 WD Raptor 74GB on a PCI SATA card and an NEC 8XDVD+/-RW My mobo is a Biostar M7NCD with a Nforce 2 400+ MCP chipset. I am using the onboard sound and LAN. I also have a WD120 hard drive in an external, powered, firewire enclosure for my data and backups.

My problem is that lately ( last 3 days) I have been getting random power-offs. In the middle of something, the PC just shuts off. This can be in the middle of a game, or while the PC is merely idling. Once or twice (out of probably 30+ occurences of this) the PC has rebooted a couple times first, but has not made it past the BIOS screen. Also, the machine refuses to power back on after it does this, I have to either unplug it or flip the switch on the PSU off then on again to get it to power back up. My temps are down in the 30s idle, with a peak of about 41C while folding and playing a game. I have completely diabled folding for now, and my idle temp sits right at 31C. I have unplugged every fan save the CPU and the one on the video card. I am using a stock AMD HSF, and no other extras. My voltage rails are wonderful (+12.4, +5.3, +3.7) and vCore is right at 1.65.

These have been the settings on this machine for almost 6 months now, trouble-free. Could it be that my power supply has finally gone to PSU heaven at only 6 mos? Or does someone have another idea?

if possible, you should try with a different psu. do you have your computer hooked up through a ups? it could be the power company's fault (they've reset my computer many times). when you say it didn't make it past the bios screen, do you mean it actually turns off while going through POST?

Yes, it actually turns off in the midst of the POST, completely dead, no fans, no nothing, not even a net connection light. Once I reset the power supply, it will power on again, but the same issue repeats itself.

Try a different psu that you know was working before.

OK ,slapped a apare generic PSU in and she works fine, time for a new one.
<gets out CC and heads for newegg> any suggestions?

Fortrons, antec, and sparkle are good brands, it will also depend on how much power you need.

i like my thermaltake purepower 420W
keeps my 12V line at 12.2 at full load with my 2.25 ghz OC from 1.8
all the other lines are great too