My first self-built system. Everything ran great for about 9 months, and then problems started happening.
1) A few weeks ago -- computer suddenly shut off while under high processor load (running statistical software). I immediately pressed the power button, which was a horrible idea, and there was a crackling sound and the smell of smoke coming from the PSU. Afterwards I replaced the PSU and everything worked fine.
2) About a week ago -- computer suddenly shut off while under high processor load. I waited and tried hitting power. The lights flickered before shutting off. I then waited a few hours and when I tried again everything worked; no problems since.
3) Today -- computer shut off again. I then tried the paperclip test on the PSU, and the fan would not turn on. I think this means that this PSU is dead, too? The power light on the mobo is still lit up when the PSU is on. Again, when I press power on the case, the lights flicker before shutting off.
So why does my computer keep shutting off under high loads? Why do my PSUs keep dying? Is there a circulation problem with my case? Is my processor not being cooled properly?
PSU -- Antec EA-650
CPU -- AMD Phenom II x4 955 965 with stock heat sink/cooler
Please list your complete system specs - makes and models. It sounds like your PSU doesn't have the power to run your system at its full load, which could be solved with a larger PSU, say 700 or 750W. Or, your PSU may be failing, and you could just replace it with a new PSU.
HD -- WD Caviar 500GB Serial ATA HD 7200/16MB/SATA-3G
Memory 1 -- Corsair XMS3 2048MB PC10600 DDR3 1333MHz (2x1024)
Memory 2 -- OCZ 2048MB PC10666 DDR3 1333MHz (2x1024MB)
Mobo -- MSI NF750-G55 nForce 750a SLI Socket AM3
Case -- Cooler Master Centurion 534 Blk Case
Video card -- Sparkle GeForce 9500 GT 512MB PCIe w/DVI
CPU -- AMD Phenom II X4 965 Black Edition Deneb 3.4GHz 4000MHz Socket AM3
PSU -- Antec EA-650 Power supply
(Old PSU that died after 8 months or so) -- Power Up Standard 550w ATX Power Supply
I don't know how it could be possible for the power supply to not be able to handle my system. I only have one hard drive and my video card is very basic (and I wasn't doing anything graphics intensive when the computer crashed).
To me that sounds like an overheating problem and it's shutting everything down for protection. I myself have used the phenom II 955 and the stock heatsink wasnt that good at keeping my temps low. I switched my cooler immediately after noticing my temps were a little on the high side. Also i swapped out my 90mm exhaust fan on the case I had at the time and went with a 120mm. A couple of options now i always use coolermaster fans they run at a nice rpm and have great cfm rates another good fan is noctua as well as rosewill. If you can i would switch out your cpu cooler first i have listed a couple good ones below and if you have a 90mm fan as an exhaust setup and have the ability to move to a 120mm i would definately do it. Also make sure to use a real good thermal paste. That antec psu should be plenty of power for that rig you have.
I believe you might have mobo problem. Check for dust/insects beneath the mobo. Check for bulging capacitors. The 650W PSU should have handled that system fine. Might need a new mobo +/- new PSU, if this one is fried. Test it on a different PC, if available.
I think icehawk940 and house70 are on to something: CPU overheating will cause the system to shut down. So I like the idea of checking for bad capacitors, cleaning dust, and re-seating or replacing the CPU HSF. Since the cheapest option is to clean the system and re-seat the HSF, you could try that first. You'll need some thermal interface material like Arctic Silver 5, or another like it. Follow the CPU and HSF cleaning instructions for the material you choose.