1st time system build Need help, Computer shuts down appx. 15 sec into boot up.

[Dave726]

Hey this is my 1st time building a system but not my 1st time working on one.

There is no OS installed due to it wont stay on long enough. I've change the PS Ram HD Video cards.  So here's the run down on what happens.

I turn it on.
It boots up to the bios stays like that for appx 10-15 sec then shuts down no error or anything.

I have a xfx nforce 780i mother board on the mother board it seems to shut down after 7F which is POST error check it seems to go to FF for a second then shuts down FF is Boot.

MY set up is

NVIDIA nForce 780i SLI Intel Motherboard
Intel Core 2 Quad Q6600 2.4GHz
4GB DDR2 SDRAM DDR2 800
EVGA GeForce 8800 GT 512MB 256-bit GDDR3 X2
Western Digital Raptor  150GB 10000 RPM
Seagate Barracuda 250GB 7200 RPM
ABS Tagan BZ Series 900W
If i can get the os in Vista 32bit

I hope i gave enough info, if you need any more just ask. Thanks for the help

[homer]

did you correctly mount the heatsink? did you use thermal paste and is it fastened securely?

[Dave726]

Yes, there was already past on the heatsink so i didnt add more and yes.

[JJ 3000]

Try a different power supply

[Dave726]

I did I used 2 different ones i even uped the PS from a 750w to a 900w.

[street1 (RIP)]

Make sure your motherboard isn't grounding out on the case.

What kind of standoffs did you use ?

[Dave726]

I used the ones That came with the case.  They are Bronze

[quaxo]

Those are brass, not bronze.

[street1 (RIP)]

Did you use the little flat washers ?

I have found it better in some cases to use small flat rubber
based washers,I buy at a hardware store.

I had an Asus board that kept grounding out until I used
this type of washers.

Of course,I am only a Woodpecker and have a small brain.

[Dave726]

no washers, Ill give those rubber washers a shot today.

[patio]

You may want to do a bench test since you will be pulling the board anyways.
I use a rubber mat for this but cardboard will suffice.

Place the MBoard close enough to the monitor for a connection.
Hook up/install only the following:

Mouse
Keyboard
1 stick of RAM
Vid card
Monitor
PSU
CPU/and heatsink.

See if the machine will boot and display on the monitor.
Pay special attention to any beeps at power up.

This test will eliminate or confirm if the MBoard may be the problem.
If all goes well you can carefully re-install everything into the case...

[Dave726]

I did the bench test everything is fine. So i put everything back together for the 3rd time and it works no more shuting down. I was able to get the OS in and all the Updates. Had it running for a good 4 hrs with no problems. I guess it was just a loose connection.

Thxs for all your help.

[street1 (RIP)]

Glad you got it fixed friend.