New computer build fails to boot.

[Antipodean]

Greetings, Today I built two new computers for a friend and as the title says, one of the two computers fails to boot.

After turning on the switch at the psu the system attempts to boot on its own without any prompt from the user via the power button, and after a second of lights shining and fans spinning, it all stops and goes quiet for 5 seconds, it then repeats this cycle, again without any prompt from myself.

After turning off the switch the computer attempts to start up a final time without power, the lights come on and the fans spin for a split second and then it stops completely. I am going back to my friend's place tomorrow to work on this computer and hopefully, get it working. It is very similar to my own computer (Same mobo, cpu, graphics card and RAM) and thus I have compared every aspect of it to my own machine and both systems are nearly identical, save for the power supply.

I plan to test my friend's power supply in the other computer that I had built for him today to check it, also I plan to re-build the entire system, ensuring that none of the metal bolts between the motherboard and the back of the case are in-properly located.

I don't have alot of experience building computers (have only built 6 in the past) so anything that you can tell me would be helpful.

I was wondering if anyone here could share any advice on the issue and offer other options for solving it.

Thank you very much in advance.

EDIT:
The computer

Gigabyte X48-DQ6 mobo
Intel Core 2 Q9550 cpu
4GB Kingston HyperX 1066MHz ram
Antec 902 case
Cooler master 650 watt psu
two 500GB seagate sata hard disk drives
one LG DVD sata drive
1GB ATI Radeon 4870 graphics

[glendalf81]

check all jumpers on the mobo, ensure they are all in the correct position, i know you said you duplicated the 2 builds but its possible you missed a jumper somewhere i have done it myself in the past

[Antipodean]

will do, thanks glendalf.

[KarmaKiller]

In my experience, a PSU that starts up without hitting the power button, is either a bad PSU. Or the actual power button is broke.

[glendalf81]

Quote:

Originally Posted by KarmaKiller

In my experience, a PSU that starts up without hitting the power button, is either a bad PSU. Or the actual power button is broke.

while that is true, just last week i built a system without instructions for the mobo and whenever i shut down it just kept booting again, and it turned out to be the start on lan jumper being closed instead of open so it kept starting as there was constantly a signal from the ethernet cable

[Antipodean]

Alright solved the problem. In the end re-building the computer did the trick. Thanks for your help folks, I'll be sure to consult techimo.com for any future queries.

Thanks again.