New HTPC build... no response seen when pushing power button

[adidosc]

I'm hoping that someone on the forums here can help me diagnose the problem I'm having with new computer I put together as a HTPC for my living room.

Problem: When I push the power button on the case, I see no response what-so-ever from the system. Not even a fan will move.

What I've done so far:

I've replaced a 600 watt power supply with a 650 watt power supply, no difference.

I RMA'd the motherboard and got a new one, no difference.

I RMA'd the processor and got a new one, no difference.

I got a different processor specifically off the Gigabyte compatability list (even though the AM2+ processor I had should have worked just fine), no difference.

I tried different RAM configurations (I have 4 sticks 1 GB each), no difference.


Now here's the kicker... when I do not have the 4 pin 12v connector connected to the motherboard, the fans DO run. Anything powered really. But of course the CPU needs this to function, so I can't very well continue on with my system build if it's not plugged in.

Something else to consider: when I put a voltmeter to the 4 pin 12v connector when it is not attached to the motherboard and power on the system, it measures 12.2v. I'm no expert, but I believe that's close enough to 12 to not have any issues.

I'm completely puzzled as to what could be the issue, and its slightly frustrating knowing all this money I've put into the system and I can't so much as see it POST. I'm hoping the Tom's Hardware readers can help me!

Thanks!

 

[adidosc]

Here's a few specs if it'll help:

CPU (on Gigabyte's compatability list): AMD Phenom 8450 Toliman 2.1GHz Socket AM2+ 95W Triple Core

CPU (original one I tried): AMD Athlon 64 X2 7750 Kuma 2.7GHz Socket AM2+ 95W Dual-Core black edition

MB: GIGABYTE GA-MA78G-DS3HP AM2+/AM2 AMD 780G HDMI ATX

Power Supply: CORSAIR CMPSU-650TX 650W

RAM: OCZ SLI-Ready Edition 4GB (4 x 1GB) 240-Pin DDR2 SDRAM DDR2 1066 (PC2 8500) Dual Channel

 

[Guest]

heres what might be a problem, look under around the motherboard to see if you dropped a screw, any kind of metal that might be touching the motherboard and grounding to the case. im no expert, but id look at the simplest thing first,hope that helps you

john

 

[Guest]

how long are your standoffs that keep the mobo away from the case? anything touching back there? does the PSU work on another machine?

new here but brainstorming: if the 12v rail is shorting, it could be putting the PSU to safety shutdown. then with 12v rail disconnected, the short is gone, PSU out of protection mode, fan runs. check your clearances between case and mobo like happyalberta said. also - is anything else touching the mobo? such as fin of cooler ...can opener (smile!), open the case, stand back and really look! when you close the case, is there anything that might impinge on the mobo? question: if the HDD is bad, will the RAM still post? seems so. build superheroes will answer soon. Stay positive. Keep looking and exploring to find the problem. reseat the RAM. look for shorts.

 

[adidosc]

You guys might be onto something, but I'll have to wait until I get home to try it. When I was installing the case, I put in all of the supports that screw into the motherboard that said ATX. But, I did notice when putting in the MB that it didn't need all of them, only about half matched up to the holes the MB had. I'll take the extra ones out and see if I can get anywhere with that.

I don't believe the hard drives are bad, but then again they're not hooked up. I have only the necessities installed and I'll work my way up from there if it shows signs of life!

 

[adidosc]

It worked! I tested it by lifting the MB off the riser pins and it started right up. I then took it out and left only the 7 in that the MB had holes for and it continued to work like a champ. Thanks guys... I just wish I would have asked this question weeks ago!

 

[jsc]

You guys might be onto something, but I'll have to wait until I get home to try it. When I was installing the case, I put in all of the supports that screw into the motherboard that said ATX. But, I did notice when putting in the MB that it didn't need all of them, only about half matched up to the holes the MB had. I'll take the extra ones out and see if I can get anywhere with that.

That may be your problem. You need one screw post for each motherboard hole - no more. Fix that. [strike]Then try swapping power and rest switches. Sometimes, the case power switch is bad. Doesn't happen often.[/strike]

While the motherboard is out of the case, place it on an insulating surface. Make sure that both PSU power connectors (main 24 pin and 4/8 pin CPU power) are installed.

Pull everything except the CPU and HSF. Boot. You should hear a series of long single beeps indicating memory problems. Silence here indicates, in probable
order, a bad PSU, motherboard, or CPU - or a bad installation where something is shorting and shutting down the PSU. (Removing the motherboard from the case will eliminate this possibility.)

If you get the long beeps, add a stick of RAM. Boot. The beep pattern should change to one long and two or three short beeps. Silence indicates that the RAM
is shorting out the PSU. Long single beeps indicates that the BIOS does not recognize the presence of the RAM. Either way, that particular RAM stick is bad.

If you get the one long and two or three short beeps, install the video card and any needed power cables. If the video card is good, the system should
successfully POST (one short beep, usually).

Note - a PSU with inadequate 12 volt output will also cause this step to fail.

Another note - you do not need drives or a keyboard to get this far.

If you successfully POST, start plugging in the rest of the components, one at a time.

Building the computer outside the case is called "breadboarding" (from the 1920's days of homebuilt radios). I use an insulated cutting board. I always
breadboard a new build. It lets me test the components before I go through all the work of installing them in a case.

 

[cadder]

I used to do this back in the real old days- mobo+cpu+ram, PSU, graphics card, monitor. This should let it go partway through the post, and you can watch it on the video. Then start adding things from there. (Back in those days there were a lot more cards that plugged into the mobo, compared to how we do it now. Hard drive controller, sound card, other ports, etc.)

 

[jsc]

Those aren't "the real old days", just the old days. In the real old days, building a computer meant taking soldering iron in hand.

About 5 years ago, I was building a "give-away system" out of recycled parts. The build didn't work. Had to pull the parts out of the case. Since then, I always breadboard.