Computer shuts down after power on

[zrush]

I just put together a new PC. I've done a few of these before, and I have never encountered a problem like this. I've searched the web and can't find anything.

Asus P5Q
Intel C2D E7200
Palit Radeon HD 3870
OCZ DDR2 800 4GB (2 x 2GB)
Antec Neo Power 500w

When I turn on the computer, it starts up for about two seconds, then shuts down. About three seconds later, it'll start up again, then shut down after two seconds. Repeat. Everything starts running during these two brief seconds. The fans are all going, motherboard light is green, everything seems fine, then it shuts down.

During the past two hours I've removed the hard drive, the dvd drive, the video card, the fans, the memory sticks (tried one in each of the four slots), put in memory from the computer I'm on now (so the memory isn't bad), placed all the jumpers in every possible position, and of course reset the CMOS a countless number of times.

It might be worth nothing that when I started without any RAM, the computer stayed on for a few seconds longer before beeping and shutting down, and then continuing the loop.

I've tried everything I can possibly think of. I'm stumped. Can you guys help?

 

[KurrentEweser]

Make sure the cpu heatsink installed correctly.

 

[zrush]

As opposed to what? Installing it upside down?

 

[KurrentEweser]

As opposed to what? Installing it upside down?

As in flush. And with thermal paste.

 

[zrush]

Check on both parts. It has an aftermarket cooler, along with Arctic Silver 5.

 

[KurrentEweser]

Does you get a bios screen at all?

 

[zrush]

Nothing. I've tried slamming down delete, F5, and F8... and still nothing. I've tried a different keyboard as well. I even went so far as to unplug my speakers and monitor, and still the thing starts up for two seconds, fans run, then shuts itself down.

 

[KurrentEweser]

You may not have the correct 4 pin power plug coming from the power supply going to the CPU power socket. Some power supplies have two four pin plugs that carry different voltages. They can easily confused.

 

[yonutzbig]

hello , i have got the same problem and i do not know how to solve it , please help : my computer shuts down after three seconds ,
a new computer
cpu quad 9300
hdd 1,5 tb
mb cp4sc-ds3r gigabyte
psu 650w speeze
vga ati 3870
ram ddr3 2gb


ok , so i try to start my computer and it start only for three seconds then shuts down then start again for three secondes an so on

a have removed all components each one , to test it , same thing
what is happening ????

please help , thank you