New system build not working

I am building my first from-scratch computer. And it isn't working.

Dear Internets: HELP!

All parts arrived. I built the system carefully & with good anti-static precautions.

I had some trouble at first, but it was all clearly my fault - must plug the PSU into the mobo by the 20+4 AND the 8-ATX, case fans should be plugged into the mobo OR the Molex... important stuff! But once it was all said and done, things seemed to be going better.

The computer would boot. It would POST clear (single beep). Launching BIOS would show all processor cores recognized and operating well and cool, all four RAM chips up and running, all drives recognized... all a-ok.

I installed Windows 7 to the SSD, booted, and it launched! Internet and USB3.0 connectivity. Beautiful.

After about 5 minutes, computer suddenly powered off. Rebooted, tried again, and... yeah. Between 2 and 10 minutes of perfect working, then it would suddenly completely lose power. No BSD, no freezing - off.

I tried playing around. I disconnected all case fans, the DVD drive and secondary hard drives. Then it wouldn't get past the BIOS. I tried plugging them back in. Same deal. I tried removing the graphics card - then it wouldn't even POST. I put everything back, and... nope. No booting.

Based on my research, I concluded that the most likely culprit was either the mobo or psu. So I returned them both. Replacements just arrived. So I put them in, rebuilt the machine, and turned it on.

POSTed successfully. BIOS showed all clear. Got the ubiquitous 'windows did not shut down correctly' message. I told it to boot normally. And - power off.

This happened three times in a row. Nada.

I tried booting windows from cd. Nothing. I tried booting Linux Mint from a Live CD. same problem.

I took out the graphics card, tried booting - nope, wouldn't POST.

I put the graphics card back in, and - still won't POST.

I took it apart entirely and put it back together. Everything seems properly connected! Then the fans spin up properly, everything looks great... but no signal to the monitor.

I try DVI, I try HDMI... nothing. I try with one stick of ram, w/o peripherals, w/o graphics card... nothing.

Then it stops getting that far. Now it powers off a few seconds after I press the on button.

The computer is in the exact same configuration it was in when it would (at various times) A) boot successfully but power off after a short time, B) power off at the launch of the gui, C) display BIOS but not get to bootloader, D) turn on but output nothing to monitor, E) power off the moment it was turned on.

I took it apart completely and put it back together again. Nothing.

I tried an on-the-box build - nothing but motherboard and PSU, hooked up to power and the monitor. And with various combinations of peripherals. Entirely outside the case. Nothing.

I've tried booting from each hard drive, from various install CDs... nothing.

I've gotten a new power supply, a new mobo, and tried every possible combination of chips and peripherals. Right now it's just a box of very expensive silicon.

Dear Internet: WHAT CAN I DO?!


The specs are as follows:

PROCESSOR:
intel core i7-3770k ivy bridge 3.5ghz lga 1155 77w quad-core desktop processor / intel hd graphics 4000

MOBO:
gigabyte ga-z77x-d3h lga 1155 intel z77 atx

RAM:
avexir standard ddr3-1600 32gb (8gbx4) cl10

PSU:
xion xon-850p14f 850w, atx 12v 2.91 & eps 12v

HELP!

-davekov