I see that the shutoff/restart by itself issue is fairly common, mine has been doing it for sevearl days. I've been through the troubleshooting from this website, starting with changing the startup & recovery option of auto restart on errors, but it STILL does it. The hardware is seated properly and I haven't added anything new or updated any drivers recently, virus & spyware is clean and it even does this in safemode. It seems to run best in bios mode. The most recent software I installed is AOL's instant messenger which annoyingly auto-installed and defaulted my browser to the AOL browser and I don't have AOL. I'm at the end of my troubleshooting knowledge and I guess now I'm hoping a format (unfortunately) and a clean install of XP will take care of this. But how in the world do you install the clean OS when it won't run LONG enough?  :-?First you check your power supply.  No point doing a fresh install if the power supply is going bad.  You could even try plugging your PC into a different socket.  See if that helps.  I'd venture a guess that your power supply is the problem.The fact that the machine reboots in Safe Mode points to an overheating problem. However, this may not be the case. What tools disd you use for the AV/malware scans?Thanks guys, I would hope it's not the power supply, it's only about a year or 2 old. I monitored the temp in the bios for about an hour and it didn't go above 52C. I used etrust for the av & pest patrol spyware, plus I used adaware after, then I used tweaknow for a registry scan. I noticed in the event viewer numerous errors for a file extension True Vector Services and iamdb.rdb, so I uninstalled the etrust firewall because I found out it was linked to those. The funny thing is it can work for a few days just fine and then start this whole shutoff thing again. When it shuts off it acts as if the plug was pulled and after 1 or 2 MINUTES it turns itself back on and reboots. In the bios screen it doesn't do the shutdown thing. This is by far the weirdest thing I've seen a pc do. I really appreciate the help!It depends on the maker of the supply as well as the current and what all is loaded on that machine. What is the make and model# as well as the reported wattage.I opened the case and there is no markings at all to tell me the make or power of the ps. I'm not sure how to tell the wattage of the ps either, but thinking back I thought I bought a 450w but I could be wrong, it could be 350w.

Here's the config:
Asus A7N8X Deluxe board
AMD XP 2.0ghz processor
Western Digital 140gb hdd
1.0ghz ddr pc2100 ram
XFX Geforce FX5200 256mb ddr nvidia graphics card
windows xp pro

I built it myself  A no name power supply that says 450w could still well be a hunk o' junk, especially with high end systems. If you didn't spend at least $50 on it I would suspect that. Do you have any way to test it?

You can check your temps with Everest for free:

http://www.majorgeeks.com/download4181.htmlThat looks good, I'm going to try to get Everest to run tomorrow after I get home from work. Will that tell me the wattage of the ps? It looks like a helpful tool at any rate so I'll run it tomorrow for sure.Well, Everest is a no-go, the pc wont run long enough before shutting down. I can just get it to where I'm signed into my xp PROFILE then off it goes, then back on a minute or so later. Is there a way I can test the ps, and if I let it run on the bios screen and it runs without restarting wouldn't that mean the ps is ok, or is it ok just on the boot and when all the components get fired up it STRAINS the ps and shuts down...ughh I'm getting a headache! How can I know how much power I need?Think Antec and 400+ watts

www.newegg.comTo test if it's the PSU being overloaded, disconnect a few unnecessary components and peripherals such as USB devices, CD drive units etc.Thanks for your help, heres the result: I added a 450 watt XG Vigor power supply (couldnt afford the Antec) and so far it's running solid, 24 hours now. The only side note is my operating temp went from 52C to about 57C, and even hotter after I play games. On my board (Asus A7N8X Deluxe) is a set of plugs, one says chassis fan & the other is a different fan. What fan do I plug there because none of my fans have that type of plug? Does anyone use the system blowers?Do you have any additional case fans in there? Take the cover off and blow a fan in there and see what the temps do and provide a clue to the solution.  The onboard plugs are probably for CPU, case and or gfx card fans. The CPU fan should be connected to the motherboard controller as it's monitored but case fans can be connected via the larger Molex type connectors.