Gigabyte P67A-UD3 single phase led no boot

[Mollins]

OK hardware configuration is:

PSU: Xigmatek NRP-PC702 700W
CPU: Intel Core-i5 2500k
Motherboard: Gigabyte P67A-UD3
GPU: ATI Radeon HD 6950
RAM: GeIL 8GB (2x4GB) DDR3 PC3-12800C9 1600MHz VALUE PLUS Dual Channel

I've been running this set up for a few months, and today all of a sudden it crashed, I wasn't doing anything intensive it seemed to just turn off, right as a started a video playing.
Tried to restart and I was getting nothing, so I lifted it up onto the desk and opened it up to have a look, when I press the power button, within the first half second of doing so a single green LED on the Phase LED lights for a fraction of a second and the fans start up for about as long as well, then it just stops.

I've tried re-seating the ram, and seating a single stick of ram in each slot (with both sticks), no luck
I disconnected then reconnected the GPU, no luck there either.

I'm not really sure what's going on, and it's a bit frustrating (and worrying), just wondering if you guys think you'd be able to perhaps shed a bit more light onto the situation?

 

[SpinMan]

OK hardware configuration is:

PSU: Xigmatek NRP-PC702 700W
CPU: Intel Core-i5 2500k
Motherboard: Gigabyte P67A-UD3
GPU: ATI Radeon HD 6950
RAM: GeIL 8GB (2x4GB) DDR3 PC3-12800C9 1600MHz VALUE PLUS Dual Channel

I've been running this set up for a few months, and today all of a sudden it crashed, I wasn't doing anything intensive it seemed to just turn off, right as a started a video playing.
Tried to restart and I was getting nothing, so I lifted it up onto the desk and opened it up to have a look, when I press the power button, within the first half second of doing so a single green LED on the Phase LED lights for a fraction of a second and the fans start up for about as long as well, then it just stops.

I've tried re-seating the ram, and seating a single stick of ram in each slot (with both sticks), no luck
I disconnected then reconnected the GPU, no luck there either.

I'm not really sure what's going on, and it's a bit frustrating (and worrying), just wondering if you guys think you'd be able to perhaps shed a bit more light onto the situation?

It is probably your power supply unit being faulty. Try the paperclip test (google it) on it with only external chassis fans connected (to satisfy the minimum load requirement for the PSU) and see if the fans keeps running. If they shut down immediately again or it fails to spin all together, then you know for sure it is your PSU.

If it passes the test, the prime suspect becomes your MB.

Oh, one more thing, make sure your CPU power (4 or 8-pin) is connected from the PSU to the MB, as well as your CPU fan is also attached the MB.

1-) It is unlikely that it is your RAMs. It would beep constantly and every fan would still be on.
2-) It is also unlikely that it is the CPU. Pretty high chances again fans would be on with no post behavior, plus you may get error codes from the LED.

Good hunting!