Computer keeps shutting down

all of a sudden my computer will not start up. i plug in the power supply to the wall and it starts up for 1 sec and shuts down immediately. i thought it was the power supply so i replaced that. but still does it will a new power supply. the fan on CPU works. my son might of been powering it on and off. i unplugged everything cept the motherboard. even took the CPU out and it does the same thing. do you think the motherboard is fried?

thanks for your help in advance.

That was happening to me once after swapping out a component. I found that my 24-pin connector was only slightly connected, and was sending intermittent power to the MB. After pushing it in all the way, it was fine. I'd say try unplugging every plug, and if needed every component, on the MB, and re-inserting it, making sure everything is seated securely. Same thing on the hard drives, too. It's worth a shot, and you might as well check everything, since it'll only take a few minutes. If that still doesn't do it, then try the last-ditch-effort of resetting the CMOS (button or removing battery). After that, I can't think of anything else besides some bad component, which takes process of elimination, like leo2kp said.

I am having the exact same problem with my computer. When I unplug the ethernet cable from my motherboard, the problem goes away. As soon as I reconnect the ethernet cable, the computer immediately powers off. I keep my case very clean. I clean the cpu fan & heatsink at least three times a year with a can of compressed air. This problem started after I downloaded some porn. Regardless of whether you believe I got what I "deserve", is there malware on my computer that's responsible for my computer shutting it down?

ePOWER ZU-550W PSU
ASUS A8N-SLI Deluxe
eVGA eGeForce 8800 GTS 640 MB
AMD Athlon FX-57
(4x) 1 GB PC-3200 DDR
Maxtor 300 GB ATA 133 7200 RPM
Western Digital 400 GB SATA
Memorex CD/RW
Sony DVD±RW

[UPDATE] I opened my psu and cleaned the fans, but now my computer won't start at all. I've checked and rechecked the connector pins from my tower to my motherboard. No power. Also, the problem happened whenever my WD SATA HDD was plugged in. When I only had my ATA133 HDD hooked up, my computer never shut down the way it does.

Hmmm.... What is Tier 3? I've already placed an order for a brand new psu, just in case. I bought a COOLMAX cuq-1200b. I hope that's a better quality product and not just some power-hungry psu. According to UPS, it should arrive tomorrow afternoon.

What?! Rats! I didn't know anything about the different Tiers. I've never even seen that website. Who are the people who grade stuff there? How can I know that it's a good site? E-Power is listed on Tier 4 of their list, btw (not that it matters now). Should I try to send it back? It will arrive later on today.

Alright, I've got an RMA number with MWave to send it back for a refund. The CoolMax psu fried my Maxtor, which was a good drive.

No, I've never heard of xtremesystems. I've also never heard of the Skultrail, either. Whatever that is. Forgive me for not being a fanboy.

At least my computer hasn't shut off since I installed the psu, so I know that the problem isn't the porn. Thanks for the help.