Boot loop

I switched on my Sandy Bridge today to do some work on it and it is in some sort of boot loop - all fans and what sounds like it looking in the optical drive for a boot source commence then stop for a few seconds then the loop starts all over again. There is no RAM beep and no graphics in fact nothing hooked up to the machine at all so I cannot even get into the BIOS.

I have tried reseating the RAM (very difficult under the large cooler) the graphics card and generally checking around inside the case and the only thing I can see are the lights on the fans and four very small LEDs that are lit up two red two green as in pic.

The odd thing is I have no beep and that the boot attempt will only stop if I disconnect form the mains power supply. Using the power button does nothing. I do seem to remember from a long while ago something about those LEDs that are lit up but all Googles have come up nothing.

The board is a Gigabyte GA-H67A-UD3H with 8GB on board and an i5 2500 CPU GTX 650Ti card PSU is fine I think - Corsair HX 650

Any ideas please because this machine has been a non problem since I built it.

Dang! That looks like one heck of a motherboard. But when an otherwise good computer won't boot up, I always pull out my PSU checker and check the PSU to make sure it's putting out ALL its voltages.
On many motherboards, if the low voltage +3.3 or -5 v is missing, it will not boot up, but lights will come on and drives and fans may spin. That's always iffy, so don't quote me on exact symptoms.
But nothing replaces a good, Digital, PSU tester to find an ailing PSU.
I also take a quick look at the motherboard, for bulging capacitors. Those dang things can kill even the best mobo's.

If you were closer, I'd say "bring it on down here and I'll take a look at it for you" and probably fix it too.
(I just replaced a bad PSU, this week, for an old customer of mine.)

Good Luck,
TechnoMage

Thanks for the reply TechnoMage now odd thing mate I have just reseated the graphics card yet again because I just out of curiosity tested with the DVI socket on the board gave me a screen albeit a crappy res of 1220x900 or some such and the machine fired up as if nothing had happened

The res is back to 1920x1080 now and the only thing I can think of is there had been a close lightning strike while I have been away and well who knows??

The PSU I did test out first up as you suggested with a digital meter at the 24 pin plug (because normally I would use HW Info software to check out the PSU stuff amongst other components) - and all actually right on the money including the Power Good cable (grey) read normal voltage which I know is missing if the PSU is out of whack.

Well stranger things happen at sea they say

Seeing that you are into this stuff this might be of interest to you I include it in a little diity for running HW Info software
Power Supply 101: A Reference Of Specifications - Power Supplies see ssection 2 rail voltages