New PC turns on and off repeatedly

[dave929]

I just finished building a PC on my own for the first time. When I plug it in and turn it on, it'll run (all the fans, LED lights, etc.) for a few seconds and then turn off. Two or three seconds later it'll turn on again and repeat the process until I shut it off. I checked to make sure no cables were loose, but it still doesn't work. Any suggestions?

Edit: Also, there are no beeps during this process.

Specs:

Mother Board:
Asus M3N-HT Deluxe/Mempipe Motherboard - NVIDIA nForce 780a SLI, Socket AM2+, ATX, Audio, Video, HDMI, PCI Express 2.0, SLI Ready, Gigabit LAN, S/PDIF, USB 2.0, eSATA, RAID

Processor:
AMD Phenom X4 9950 Quad Core Processor HD995ZXAGHBOX - Black Edition, 2.60GHz, 4MB Cache, 2000MHz (4000 MT/s) FSB

PSU:
Ultra X3 ULT40311 1000-Watt Power Supply - ATX, SATA-Ready, PCI-E Ready

Memory:
Two - OCZ SLI-Ready Dual Channel 4096MB PC6400 DDR2 800MHz Memory (2x2048MB)

Graphics Card:
Two - XFX GeForce 9600 GSO Video Card - 768MB DDR2, PCI Express 2.0, Dual Link DVI, SLI Ready

Hard drive:
Seagate 1.5TB Serial ATA HD 7200/32MB/SATA-3G

Case:
NZXT Tempest ATX Mid-Tower Case

 

[Shadow703793]

1. Make sure all power connectors (ie 4 pin CPU, GPU PCIe) etc are connected.

2. Did you use the motherboard stand offs?

 

[dave929]

they're all connected, and yes i used the motherboard standoffs, though im not sure if i correctly placed the cardboard washers that came with it

 

[Rohsiph]

I'm having basically the same problem with a pretty different system:

GIGABYTE GA-EX58-UD4P LGA 1366 Intel X58 ATX motherboard
Core I7 920 processor
Sapphire Radeon HD 4870 1gb vid-card
3x1gb Crucial DDR3 1066 ram
PC Power & Cooling S75CF 750W PSU
Seagate 1TB SATA HD

System will stay powered if I remove all ram or hold down CMOS button, but won't post.

Seems like there must be some kind of short on the MB, but as far as I can tell everything's connected properly . . . what's the usual diagnosis for this kind of problem?

 

[aford10]

You don't need cardboard washers, the brass standoffs if placed properly will ground the board. ASUS boards usually have an internal speaker to give off beep codes, do you have that plugged in correctly? If you aren't getting any beep codes or light codes, it probably isn't even POSTing. Check your cables for exposed metal touching case/hdd/psu anything that's metal. If that is all good...

Boot with only 1 stick of RAM, video card, HD, and make sure cpu is seated properly.

 

[dave929]

I booted with 1 stick of RAM, video card, and HD and it stayed powered on for a little longer, but then shut off again

 

[infeckted]

Make SURE that your heatsink is put on correctly. Don't take it off, but try to wiggle it, and see if it moves a lot. If it does, then you installed it wrong. This happened to me when I first built my system. It would stay on for like 30 seconds and then turn off.

 

[dave929]

yeah the heat sink is fine.

after a little trial-and-error I think I narrowed it down to the motherboard being the problem, as every other piece will run fine