All right, this problem started about a year ago. I had been running XP for about a month or two, and then the PC suddenly started crashing. Not freezing - a complete power loss. I tried everything...system temperatures, replacing RAM, with and without a UPS, etc. The last thing I could think of was a complete reformat. I did this, and since my XP cd was scratched I installed 98. Magically, it was fixed. I was happy. So a couple of weeks ago, I installed a linux distro on a different partition. It worked great, except it was crashing just like it used to. I decided maybe it was the power supply after all, so I replaced it with a 400w. This seemed to fix the problem in linux, but now 98 would crash. Didn't make sense to me, but I thought that maybe if linux worked with the new PS, maybe XP would too. I re-upgraded with a friend's CD, but XP still crashes. This is where I am now. I have tried just about everything under the sun. I've toggled every BIOS setting that could possibly have anything to do with it. (XP won't let me turn off ACPI, but I tried that under linux and 98 and it didn't help) I have the case open to keep it ventillating, and the system is well within limits. Disabling on-board sound seemed to help, so did turning AGP settings down, but it's almost like the problem adapted and it's back to full strength. Any ideas would be appreciated. Win XP Professional, fully updated NVidia GeForce 2 Ultra 64 mb SBLive Value Athlon AMD TBird 1.33 512 SDRAM Liteon cd recorder, generic dvd player 3com ethernet adapter Thanks, Taylor

next time it crashes check the voltage on pin14 of the power supply. if it's floating, (not solid ground, 0V) then the PS is being told to shutdown. here's a reference. ATX PS if pin 14 looses it's ground for even a blip, like a questionable connection, it shuts off. you could try wiggling that wire on the MB side (it's the only green wire)

Thanks for your reply. I checked the voltage on pin 14 when the computer crashed and there was no voltage, it was 0. While I had my voltage meter out I went ahead and checked some of the other wires, namely the 12v yellow wire and a few random 5v ones; they read correctly and stayed stable even under heavy processor load. So what you're saying is that it has an unstable connection, or at least that it's a power problem. I would agree with that diagnosis, but it's hard for me to swallow since it's happened on two different power supplies and I've had this hooked up to a UPS the whole time. Though, I have tried it without the UPS and also at a different outlet. Could it be that the flow of electricity dips down slightly, say when the washing machine starts, so as not to tell the UPS to activate but to make the computer shut off? Thanks again for your help. Taylor

By the way, there is one interesting thing that may be related. After I replaced the power supply, when the computer crashes you can't just turn it back on. You first have to hold the power button in for about 5 seconds - as if you were turning it off - and then the lights on the case blink, and you can hit the power button again to turn it on. It's as if it's not really off, but of course it is - no sound, no fans spinning, no power lights, etc. Thanks, Taylor

"So what you're saying is that it has an unstable connection, or at least that it's a power problem" I don't know but it needed to be eliminated as a suspect. It could also be the connector on the MB but now I don't think so. "Could it be that the flow of electricity dips down slightly, say when the washing machine starts, so as not to tell the UPS to activate but to make the computer shut off?" unlikely. the power supply just draws more current to make up the difference and maintain output voltages. The AC would have to dip below 90 volts before real problems occur. "After I replaced the power supply, when the computer crashes you can't just turn it back on. You first have to hold the power button in for about 5 seconds - as if you were turning it off - and then the lights on the case blink, and you can hit the power button again to turn it on. It's as if it's not really off, but of course it is - no sound, no fans spinning, no power lights, etc." Now THAT's interesting. A BIOS setting controls the delayed power off to prevent accidental shutdown. If it were disabled, shutdown would be immediate. How about your ACPI settings? look at this: Sleep Mode another possibility. do you have remote administration enabled? you could be forced into hibernate mode remotely. Even though you said it does this in XP and Linux the capability is still there. Have you scanned for viruses with some more aggressive scans like AdAware SpyBot ? When you run these be careful what you delete. 1 rule of thumb, if you find something that has an uninstall listing in Add/Remove programs, remove them that way. these routines are ruthless in their pursuit of nasties and you could crash your system if you remove the wrong things. be very mindful of registry changes.

I do agree that the power button delay is interesting. Especially since my BIOS has that feature turned off. I believe it calls it something like "Soft Off PWRBTN", which has option choices of "4 second delay" or "instant off". Even when set to instant off, you still have to hold the button in after it crashes before you can turn it back on. ACPI settings check out, and when I was running Linux disabling ACPI did not solve the problem. I have the suspend type set to S1, not S3. S3 is the Save-To_Ram method, which is the one that shuts off the monitor and fans. I don't think that the computer is going into suspend or hibernate mode. On some occasions the computer will crash before it is even fully booted. As to a virus, I'm not sure. I have run checks in the past for this problem and it didn't find anything. Additionally, the problem survived a reformat and a BIOS flash, so I don't think it's a virus. What is the possibility that it's a video card problem? Turning down AGP settings did seem to help some, making the frequency of the crashes less. And failing that, could it just be a bad motherboard? Thanks again for your help RayMan, Taylor

Agreed. Another thing you mentioned is that it's ignoring the BIOS settings.If you get to the point of replacing the MB try flashing the BIOS first. It couldn't hurt. If it fails to flash then maybe somoething is wrong with the BIOS chip itself.