custom PC won't start after a few upgrades

[DefZeppelin]

I just upgraded the PSU and video cards in my custom-build PC (which I built about 2 1/2 years ago). Whenever I turn it on, all the components power up (all the fans spin, lights on mobo light up, hard drive and dvd drives start buzzing), but the motherboard will not beep and neither the BIOS nor the Windows 7 OS will boot up.

I've had this problem before with the old build, at first only occasionally, but over time it became more and more common, to the point where I often have to restart the computer four or five times before it would actually boot up normally. After I put the new components in, it won't even boot up at all.

I've fiddled with all the connections and gave the whole rig a thorough cleaning. Everything is connected correctly and securely. The computer will start up with the old video cards (though it takes a couple tries still). And strangely it will eventually start up with only one of the new vid cards installed, but not both. After I get it to start properly with one of the new cards, it will start briefly with both put in, but the rig will either freeze up or lose video signal and crash after a few minutes, and wont start again until i remove one of the vid cards.

Am I overloading the motherboard? Has anyone had this kind of problem before? And how can I fix it without having to buy a new motherboard? Any advice will be appreciated.

The new build is as follows:
Processor: AMD Phenom 9850 Black Edition, 2.5 GHz, Quad-core (and cooled with a Cooler Master V8)
Motherboard: Foxconn Destroyer
Video Cards (x2): MSI N460GTX Cyclone 1G5D, 1 GB GDDR5
PSU: Thermaltake Toughpower Grand 1200W
Hard Drive: Western Digital WD6400AAKS-75A7B0, 640GB
Memory (x4): Patriot Viper PVS24G8500ELKN, 4 GB (2 x 2 GB) DDR2, 1066MHz (total of 8 GB memory)
DVD Drives (x2): LiteOn 22X, iHAS422-08
Case (if it matters): Cooler Master HAF 932
OS: Windows 7 Ultimate (originally Windows Vista Ultimate, upgraded to 7 about a year ago)

Old build was identical except:
Video Cards (x2): ASUS EN9800GTX+, 512 MB DDR3
PSU: Thermaltake Toughpower Cable Management 850W

If anyone can shed some light on this, I would appreciate it.

[liljim]

It does sound like the motherboard is on its way out but i would make sure you didnt miss and power connections. Some boards have a 4 pin molex connection to help with high power demands, they will boot without it but will act as your describing. Something else to check is the psu rails, spread the load across all 4 of that power supplies rails as best you can. The real problem though is that this was happening before you upgraded which to me is what points straight to the board. I know thats not what you want to hear but theres a new board in your future.

[DefZeppelin]

I triple-checked the power connectors. Everything is secure and correct. The new PSU only has two +12V rails (one 40A, the other 85A, combined power max 1200W). The 40A rails is wired exclusively to power the motherboard and processor. The 85A rail is wired to power everything else: anything that uses PCI-E, SATA, or Molex power. I looked up the loaded power draws on all the components and did the math, and I am still well inside the safe-zone even on the one rail.

Over the past several hours I have been experimenting with card placement. There are two primary PCI-Ex16 sockets on the board (colored red). The other two sockets (blue) I read are secondary or something, and I cant place the cards in them anyway because of their physical size getting in the way of other components. It seems that when any card is in the top main x16 socket, regardless of whether it is by itself or if there's one in the bottom, nothing works. If any card is plugged into only the bottom main x16 socket, with the top empty, it works sometimes. I've tried this with all four cards, both old ones and both new ones, and I get the same result.

I didn't know if this additional information might help.

This is an image of the Foxconn Destroyer motherboard I'm using for reference.

[liljim]

sre you using any other card? sound, wifi? Im wondering about a possible irq conflict.

[DefZeppelin]

No, that's it. Everything I'm using is listed there.

Wifi is through a USB adapter device I have plugged in on the front of the case. And I just use the motherboard's on-board high-def sound device, which works fine for now. I was planning on getting a sound card later, but it's not a priority right now.

Just to rule it out, I've tested the memory also. All memory sticks are functioning, and when the rig is on, it is recognizing all 8GB of it.

[DefZeppelin]

It's finally working now... It is still very slow starting up, and doesn't output any video signal until Windows reaches the desktop, but I guess it is fine now.

Thanks for the advice though.