Newly built computer powers on...then off right away

Vorpal

No beep tone. (Although - do you have to have the front panel speaker cable connected to hear a beep tone? I'm not sure mine is connected properly - I heard the little down triangle marked the negative wire, but on mine it marks the colored wires and usually the black/white ones are the negative wires)

Anyway, at this point I've disconnected everything from the motherboard (video card, RAM, hard drives, optical drives, mice, keyboard, etc)

The CPU fan, system fan, and power supply fan all spin for a few seconds, then stop.

I have the GIGAYBTE Z68X-UD3H-B3 motherboard http://www.newegg.com/Product/Product.aspx?Item=N82E16813128498

and the intel core i5-2500k CPU

Both the motherboard and cpu are brand new. I'm trying to put them in my old case with old power supply Antec Sonata III http://www.newegg.com/Product/Product.aspx?Item=N82E16811129024

Power supply was working fine 3 hours ago.

I seek guidance on troubleshooting methods to see what is causing the failure. No beeps makes me think the mother board is shorting out. I've checked for errant wires and screws and haven't found any.

Vorpal

I just plugged the power supply cable into my old motherboard (with old cpu still attached) and everything spun up properly.

I can see a couple possibilities:

hardware incompatibility. My motherboard and processor should be compatible
PSU incompatibility? I'm using the power supply that came with the antec sonata III case, which is a 500W 12V power supply, which should be good for the motherboard
Bad motherboard or CPU?

---

Took off the cpu. Same issue.

Only have the motherboard connected to the power supply via power cable, the front panel power switch connected to the motherboard, and the system fan connected to the motherboard. Power on, fans spin for a few seconds, then stop.

Switch in old motherboard, fans stay on. Would this mean I got a bad motherboard? Or that my power supply is just not good enough?

Foomy

did you plug in both power cables? modern mother boards have a secondary cpu 8pin power cable in the top right corner over by the cpu. that's the usual cause of your problem on new builds.

Vorpal

Nope, I'd missed that one. My older motherboard didn't have it Thank you for the pointer!

That seems to have helped, certainly. Now when I press the power switch, it turns on (PSU fan and system fan spin and phase LED lights light up) for about 20s. Then it turns off for about 5s, then turns back on for 20s - it turns back on without me touching anything.

I've not seen this behavior before. Does it act that way because it's just a motherboard and there's no CPU/RAM installed?

Foomy

yes, computers won't boot into the bios without a cpu/ram

Shazkar Shadowstorm

exact same think happened to me before with forgetting to plug in the 2nd power cable to the mobo
and my friend who told me how to fix it also had the same problem

whoops

Donovan Puppyfucker

I quadruple checked that I had the CPU 8 pin plug in before I installed my CPU cooler, because it blocks off the plug.

Hell I checked everything three times before I tried powering it on the first time, and it worked perfectly!

Moral of the story? Being anal retentive about things I build/fix/modify occasionally has it's advantages.

TheCanMan

The exact same thing is happening to me, except my power-cycle is only a couple seconds. I don't even get to the motherboard splash screen, let alone BIOS. At this point I'm assuming it has to be the motherboard that's shorting somehow (this is a year old build that suddenly started acting up for no reason). I even have RMA approval from Gigabyte to send the board in for repair.

But does anyone know a way to check the 8-pin (mine's actually only using a 4-pin) CPU power from the PSU? This could be helpful for both myself and @Vorpal in diagnosing the problem. I frankenstein'd my new PSU into an ancient PC and it powered up just fine, but that didn't use the extra CPU power cable. If we could confirm that the CPU is getting the proper voltage, that'd go a long way in determining if our problem is the motherboard or the PSU.

EDIT: Actually, I may have answered my own question with a quick google.

Foomy

Ya that's what I was going to suggest, getting a multi-meter and checking the voltages on each rail would be the only way to see if your psu is working well or not.

Vorpal

@Foomy you have saved me, after plugging everything back in it all works fine. The missing 8 pin cable was the culprit.

@TheCanMan I don't remember, but I think with just the 8 pin plugged in and not the normal connector the cpu fan spun?

If you think the motherboard is shorting look for loose screws underneath the board, screws inserted in post holes where there is no post. You've probably alread checked that, but it's easier than testing each rail on your PSU

TheCanMan

Vorpal wrote: »

@Foomy you have saved me, after plugging everything back in it all works fine. The missing 8 pin cable was the culprit.

@TheCanMan I don't remember, but I think with just the 8 pin plugged in and not the normal connector the cpu fan spun?

If you think the motherboard is shorting look for loose screws underneath the board, screws inserted in post holes where there is no post. You've probably alread checked that, but it's easier than testing each rail on your PSU

Nah. My build is over a year old. Everything was put together properly. And I did check my PSU voltages and every single one of them was accurate. I just mailed out my mobo to Gigabyte.