Computer turns off by itself, then won't turn on again?

[peterd]

Hello,
I've got a problem.
Heres my setup:
epox 8kha+ (bios is from jan. 2002 I believe when I bought it)
amd 1600xp
antec 840 case (400watt)
pal 8045 heatsink with fan
geforce 3
512 MB ddr ram
4 fans (2 in back, 2 in front)
maxtor 40 g hard drive
Windows 98se
I'm not overclocking. Temps around 40-45 C.

A few months ago the computer just suddenly shut off. I would press the on button and it wouldn't power up, no fans or anything. I opened it up and kind of wiggled the power on/off connector a little on the MB, and it started again after about 15 min.
It never did this again, until this morning. So I tried the wiggle method and that didn't work. I tried to wiggle the power button on the front of the computer and that seemed to work.
But then a few minutes later it turned off again. Power button wouldn't power on. I try and move around the case power supply wires, make sure the cords are connected good, still nothing.
I'm pretty new at troubleshooting computers and this is my first build. I tested for a virus but didn't find any. At first I thought it was the MB connections with the case, but now I'm not too sure about that.
Then later in the day after work, it started up fine and about an hour later it shut off again, and wouldn't turn on. I tried to short the two pins on the power connector that is on the MB with a flathead screwdriver but it wouldn't do anything. I tried to switch the power connector around and tried wiggling again, opened the front of the case and wiggle the on/off switch a little bit, but still nothing.
I noticed that when I would unplug the power cord in the back of the case, then plug it in a few minutes later, and then try to turn the computer on, the fans would spin just for a second, then they would stop spinning. That was all that happened, just a few spins of the fans. Its pretty weird. I have good voltage at the power strip.

Could anyone give me some advice on what else I could try to see whats going on here? Thanks
Pete

[morriswindgate]

The fact that it shuts - off by itself indicates an overheating problem and the way you describe it, I would say that you have a power suppy going out. Although it could be that the CPU is over-heating, which I doubt, but anyway make sure that the HSF fan is spinning. But it does sound like a power supply.

[peterd]

Thanks morriswindgate,
I did notice that the HS fan was spinning, or has been spinning. I was also noticing that the temps were rising as I was on the computer yesterday, the last day it was running, I think the last time I checked during the last hour of running, it was reading around 47 C. The temps here were in the 90's F. so it was pretty hot. I also checked my bios settings and noticed that I didn't have the auto shutoff for a cpu temp of any kind. I also wrote down these voltages:
vcore 1.77v
vagp 1.53v
+5v 4.94v
+12v 12.34v

Then about 15 minutes later it died.
Is there a way I can check the power supply with a volt meter or some other way maybe?
Thanks.

[morriswindgate]

http://www.compute-aid.com/atxspec.html

[peterd]

Thanks again. From the acticle, do they mean that I can short the two pins on the motherboard, or are they talking about the connector coming out of the power supply?

[morriswindgate]

They are talking about the ATX connector on the power supply as shorting these two pins (Completeing the circuit) turns the power supply On

[peterd]

I was able to short the two pins on the 20 pin atx connector and the fans started up, but they only worked for a second. Should they keep spinning or was it a good sign that they only spun for a second when I shorted the two pins?

[morriswindgate]

Should keep running as you just turned on the power supply as if you were pushing the button on the case. Looks like a bad PS.

[peterd]

Thanks for your help morriswindgate. I'll be getting a new one.

[glc]

You can't rule out other components overheating such as the video card, this can cause an overload which causes the power supply to shut down in self defense. If a replacement power supply doesn't fix the problem, I'd start looking this direction.