Power cycles off and on in new build

(Second time rewriting this because it logged me out.. blah)

Hi all --

I'll preface this by saying that while I have replaced and added a bunch of components to computers before, this is my first completely new build. This is what's inside:

CPU: i5-750
Motherboard: Gigabyte GA-P55M-UD2 uATX Intel mobo
RAM: Corsair XMS3 4GB (2x2GB) DDR3-1600
PSU: Raidmax RX-730SS
HD: Samsung 1.5TB EcoGreen HD154UI
Disc Drive: Lite-On BD Combo iHES208-08
GFX: Gigabyte GV-R467ZL-1GI Radeon HD 4670

I put everything together inside this dandy HTPC case and when I turned it on the power turned immediately back off and began to cycle about once every two seconds, staying on for <1s and then trying again. The LED's all come online and all the fans start spinning for a second.

This is everything I did in order, the same issue occuring each time:

* I removed the graphics card
* I removed the HD and Disc drive
* I removed the RAM
* I removed the CPU fan and CPU, reseated it, carefully removed old thermal grease with a little alcohol and applied it new, and reattached the CPU fan.
* I replaced the PSU
* I removed it from the case
* I reset the CMOS settings
* I tried booting it by shorting out the power pins instead of using the switch

Since there is only the motherboard and processor left, I have to assume one of those was DOA. Or I am just putting the heat sink on incorrectly, but the picture matches what is in the motherboard's manual and I have no idea what else it could be. I am using the cooling fan that came with the processor.

Do you know of any ways that I can determine if the problem is the motherboard? Or anything else that might be wrong that I can check? I do not really want to RMA both the mobo and CPU if I can help it, I got them from different places and I'm sure the CPU in particular would take forever.

Thanks for reading!

It's more likely to be the motherboard than the processor, but the only way to know for sure is to replace one. If you have a local PC repair shop it might be worth stopping in and asking them to diagnose the problem. You'll probably be looking at a $50-$100 diagnostic fee, but they'll have the spare parts necessary to tell you what the problem component is.

My first guess would be a power issue, but it sounds like you've already investigated that route to some degree at least. Make sure you have both the 20 pin and the 4 pin power connectors plugged into the motherboard. Also double check that all of the power connectors are plugged in correctly and fully. Although fairly rare, it's also possible that the particular power supply you have doesn't like the power that's being fed to it from your wall outlet. Verify that your location provides the correct type of power, and potentially try a different outlet, room or building to see whether that might be causing the problem.

My second guess would be a heat issue with the processor, but it sounds like you've correctly installed the heatsink and fan. The retail hsf should be sufficient.

My third guess would be a manufacturing defect in the motherboard. The processor is also a possibility, but motherboards have more components that are likely to break than a processor.

Thanks for replying so quickly

I thought it was a power problem from the beginning, especially because I heard this was a not-so-great brand of PSU after I bought it. I bought a new Antec 500W PSU today and plugged it in because I was pretty sure that was the issue, but no go. I originally had all 24 pins of the Raidmax plugged in when I first started it, but I only did 20 of the Antec because I was just trying to get it to boot up and I thought that'd be sufficient.

I am thinking I may just take your advice, pony up the cash and take it to a local repair shop. I guess that shows me for trying to build my own machine!

Generally speaking, pins on computer components are not optional.


I ended up taking the first machine I built to the repair shop as well, turned out the stick of ram was incompatible. It registered with the motherboard which stopped the board from beeping about missing ram, but the ram prevented the board from booting into the post. Since then I've built 5 machines without running into a problem I couldn't fix.