Is my motherboard or PSU dead?

Hey guys, so I'm running a LEPA 1600w PSU and a gigabyte FM2 a85x up4 board, with a single corsair 8gb stick of ram, 80gb sata hard drive, and an A4 processor.

This rig was originally running x5 MSI 7950's without a problem, but two were a little warmer than the others, 5 degrees higher, and the 6th card was dead. So I said the hell with it, I'll have all 3 replaced...

Well, when the new ones got here, before I swapped them in I plugged in a kill a watt meter and realized I was pulling 1520w give or take with only 5 cards and there was no way I'd hit 6 cards with the current settings.

I tried undervolting in cgminer (running ubuntu 12.04) and no luck, even though I know for a fact afterburner in win 8 or 7 will do it in a second. Very frustrating. So the next thing I tried was gpu bios flashing, I figured I'd try them on a card that was running warm that was going to be replaced just in case something went south. Well it turns out it did, I wasnt able to actually edit any 7950 bios, because you can't just edit 7000 series bios these days. And so in an attempt to get a lower voltage was flashing other 7950's bios, stupid, I know. This led to a 15% decerease in hashing power, and the same damn voltage. So no progress, in attempt to grab the bios off another card, no issues there, I wasn't able to flash it back to the card I messed up. So at that point I just pulled it out and said this one is going back, period.

So I swapped in two new cards with the bad bios one and the other warm one. I also switched the powered risers I was using, some of you may have seen my last thread about how they were poorly made/soldered and caught fire. I was about to go away for 5 days and leave these running, so I thought lets not take any chances, and I switched out the powered risers.

At this point all sorts of interesting problems started happening. Long story short, only 4 would run stable now, and I had to leave for a trip and didn't have time to mess with it. I just got back the other day, and still really don't have to much time till this weekend and have just been running it with those 4 cards to get some kind of work in.

But NOW a new serious problem has arrived. After about 12-15hours the whole rig just shut off ,cold turkey, this happened sunday night into monday monring, and then monday morning into tuesday morning, and now this morning it is off again. However, after checking all connections and re plugging everything including the PSU and power cable. IT WON'T TURN ON.

It turns on for like a second the cpu fan spins a few times and not a second later it just stops.

My question is, is this the PSU failing, or have I shot the motherboard.

With 4 cards running I was only pulling 1150 on the meter, no where near the 1600.

I know that's quite a story, but members usually want as much detail as possible to give as educated/accurate answer as possible.

Thanks,
Greg

UPDATE: If I pull all the cards and risers out, it does boot. So maybe the risers?

UPDATE2: Swapped one of the powered 16x to 16x risers with one of the older ones from the batch that had one catch fire. I added some hot glue around all the contacts to keep them in spot, system booted and is mining now with all x4 cards.

I think these other powered risers I was using aren't pulling any power through the 12v molex adapters, and to much power is getting pulled through the board. That's my best guess. If someone could link a good step by step how to make your own powered risers, I think I might give that a shot.