Motherboard compatiblity question.

Hello and welcome to the forums  
i7 860 is a Lynffield CPU not a Nehalem one.
About the motherboard,yes its a good board and has good reviews

Nehalem is Intel's CPU architecture which features an intergrated memory controller - Core i7s, Core i5s and Core i3s are all part of the Nehalem architecture.
Lynnfield is just the codename for the Core i7 800 series CPUs. I'd say you're worrying over something completely irrelevant.  

The Gigabyte P55A-UD3R is a good choice - SATA III, USB 3.0, pretty decently futureproofed. But mind you, if you want to CrossFireX/SLI two cards, I'd get the P55A-UD4 - it has two 8x PCI-e lanes which won't bottleneck your graphic cards. If you actually want to use USB 3.0 and SATA III, though, your graphic card will only run at 8x, and the second PCI-e 16x lane will be disabled, also meaning that CrossFireX/SLI will be disabled too.

If you want SATA III and CrossFireX/SLI - you'd have to get a board like the ASUS P7P55D Premium or Gigabyte P55A-UD7.

When get your computer examined at the shop and they tell you, "You need a new motherboard," what they really mean is "We have no idea what the hell is wrong, so let's take a shot in the dark and hope it works better when we put everything back together." It's a real go-to answer for any problem that basic testing doesn't solve.

What this sounds like to me is honestly some kind of power issue, not a motherboard issue. This could happen if there's something wrong with the PSU -- faulty unit, one of the rails is overloaded, or the PSU just isn't big enough in the first place. What are the rest of your system specs, particularly the PSU and video card?

You also see this kind of thing happen sometimes when a motherboard is shorting against the case. Good way to check that would be to try and boot the machine briefly with the motherboard removed from the case and sitting on a non-conductive surface.

I have also seen this problem occur when there's damage to the motherboard -- one time a screwdriver slipped out of my hand and I accidentally chipped the back of the board, unfortunately right across a couple of the traces. After that, the machine would do basically what you're experiencing -- power up for a split-second and then die. So giving the motherboard a careful once-over for miniscule damage like that would be beneficial.

One other thing that's rare but can (and does) happen is a problem with the power switch on the case itself. This is usually something that a repair shop will miss because it's not what you'd think to look for and they kind of assume that's a part that will work. If the switch or the connecting wires are faulty, it can do all sorts of things, though it's most common for it to either not start at all (dead switch or wires), start then shut down after 5 seconds (continuous "depressed" signal that the machine thinks means you're holding the button down), or take several tries to start (something is not making good contact). To test for any of those things, remove the connectors from the motherboard header and try to start the machine by shorting the two appropriate "power on" pins with a flathead screwdriver.

Basically, look at all of these options before buying a new motherboard. And ASUS tends to make quality stuff; I prefer them or Gigabyte over just about anything else when building my own stuff.

Thanks for the answers guys,

I have tested the motherboard out of the case myself with just the CPU, graphics and RAM in place, and still had the same problem (and was shorting the two pins). I was also told it was tested with different working components and still nothing.

The PSU I have is a NorthQ Black Magic 850W, so its not a power problem unless it is actually faulty. And the graphics card is a Sapphire ATI Radeon HD 5850.

Perhaps I'll try and get hold of a different PSU just to test it anyway.

My main question was answered anyway, so cheers guys.