X99 UD4 playing dead

[Genesis1]

Got a strange problem which started a month ago. Been running my system OK for around 10 months or so. Currently not overclocked with just xmp on for corsair ram. One morning had been using my pc as normal and turned it off as normal. Came to switch on later in the afternoon and it was completely dead. Usually when I flip the psu on at the back the light on the graphics card cones on green. This time it blinked a fraction of a second and stayed off. I tried again. Switched off then on the psu at back....gpu blinkeed and then nothing. Pressed the case button...no life nothing. Began disconnecting hdd ram etc...tried connecting another psu and another graphics card...still no change. So cleared cmos. No change. Removed battery for 5 minutes and also replaced with fresh new battery. Then added 2 sticks of ram. Flipped psu on and graphics card light lit green. Pressed case button and everything booted as normal. Next I added the remaining ram. Boot loop. Must be a bad ram stick. Just to be sure I cleaned all ram and left offending 2 sticks out. Next day I returned all the ram to the machine and everything booted OK. It ran as normal for another 2 weeks....then I turned on the psu at the back one morning and it was dead again. Removed battery for 3 minutes and put it back. System booted fine again.
I have no ideal what causes this random playing dead behaviour and when I say dead I mean completely dead? No power to anything.
I can only think that because flipping out the battery clears the bios that the bios has a fault somehow which from time to time stops the power to the motherboard but never heard of this. Anyone have any ideas? 
Ga X99 UD4 f20 bios. 16gb corsair pc2400 ram Corsair r300 case and corsair 600m psu.

[ElectroStingz]

Hello,

The next time this occurs do not power off the PSU.
So lets say you turn on, the green light flickers.
Leave it like that, unplug the 24pin ATX and 8pin EPS connector from the motherboard.
Short the green and black wire on the PSU to see if it powers on the PSU / hard drives.

https://www.youtube.com/watch?v=5FWXgQSokF4

http://www.smps.us/atx-connector-20-24pin.jpeg

The reason for doing this as is occurs and not powering off the PSU is to see if a protection circuit was tripped within the PSU. If tripped, when you try to short the psu it will not turn on. Disconnecting the power from the PSU will reset this circuit so you must leave it connected when the issue occurs.

This tells you that there is a physical fault.
If powers on, the motherboard is causing your issue.

Whilst looking, check all the pins in the ATX/EPS connectors / board and PSU to see if there is any signs of burning.

[Genesis1]

Hello,

The next time this occurs do not power off the PSU.
So lets say you turn on, the green light flickers.
Leave it like that, unplug the 24pin ATX and 8pin EPS connector from the motherboard.
Short the green and black wire on the PSU to see if it powers on the PSU / hard drives.

https://www.youtube.com/watch?v=5FWXgQSokF4

http://www.smps.us/atx-connector-20-24pin.jpeg

The reason for doing this as is occurs and not powering off the PSU is to see if a protection circuit was tripped within the PSU. If tripped, when you try to short the psu it will not turn on. Disconnecting the power from the PSU will reset this circuit so you must leave it connected when the issue occurs.

This tells you that there is a physical fault.
If powers on, the motherboard is causing your issue.

Whilst looking, check all the pins in the ATX/EPS connectors / board and PSU to see if there is any signs of burning.

Thanks, will try that. However, what I did do at the time was disconnect the psu and connect the 24 pin and 8 pin of another psu exact same make and it still showed the same symptoms. This makes me think it's a motherboard problem.
I hardly disconnect/turn off the psu now through fear of it not booting again.
This problem is intermittent so is very hard to fault find. As I mentioned, only a CMOS reset seems to cure it.

[Genesis1]

Btw...if the protection circuit is reset when the power is turned off...shouldn't that mean that simply turning off the psu and then on would clear this and the system should boot? This did not happen and as mentioned I tried another psu. It just seems to me that something stops the power from getting through the motherboard, which is weird. Maybe a dodgy part on the motherboard somewhere??

[ElectroStingz]

The protection circuit is part of the PSU so when powered off or switched over to another PSU it can always occur if the motherboard is causing the fault. From what you have described it does seem like your board is causing the fault and the idea of the PSU test is to determine where the problem may lie.

If not tripping due to a physical short, the other areas are anything startup related.

The CPU startup voltage, VRM is another point that can cause the board to power on / off instantly.
Also points to a failing board.

Faulty CPU temp senor...

If you want to start somewhere, go for replacing the board.

[Genesis1]

It's really weird....I've left the power switched onto the board majority of the time now. Only time I risk switching off at the plug is if a storm is forecast. As long as I don't turn off all power completely I don't have a problem. As I said, it's very intermittent anyway. May not happen again for weeks or months so difficult to say.

 I'm gonna check CPU voltage though. I've not changed this at all, but I have a feeling in the back of my mind after reading and watching YouTube videos it may be higher than normal. Just for clarification. What should the CPU voltage read at non overclock setting but with xmp memory activated at 2400?

[ElectroStingz]

Depends on the CPU, Broadwell-E would be around 1.2v-1.325v range with load / turbo boost.