Odd computer crashing under load

[Xsarith]

Hi there, I've been using these forms for years now but its the first time I've ever posted anything on here. Anyway I've been having an issue that I can't quite solve and google hasn't helped me much as the symptoms are similar to overheating.

So under load (using FurMark) after 4 minutes my computers screens would go off, the fans would roar for less than a second and then calm down and my computer would remain on, but unresponsive and without sound, as though it had completely crashed and lost display signal.

Please note that this first happened while playing games and I suspected overheating so I tested that with FurMark with HWmonitor open on top watching the temperatures until it happened. The GPU got to 80c and then it happened, it's an R9 290x which I've ran at over 100c before I got my hydro H50 on it, and everything else was well below their shut off points too.

I then suspected insufficient power, I have a corsair 750M which was enough when I built it, and up until recently its been working fine, theres been no hardware changes either other than adding a hydro cooler to the graphics card which again was working for months without an issue. So I also aren't fully convinced its that.

I then had a break through, after resetting the Bios to optimised defaults, and only setting to Ram to its correct speed then the fans kicked in louder and so I ran the test again and the GPU struggled to reach over 68c and reached 8minutes in the test as well. That then confirmed that overheating isn't and issue and also made me doubt the power insufficiency also.

I've tested a few other minor ways also, just basic troubleshoots but is there anything else I could try. I borrowing my buddies old pc and I'm going to use that to start swapping out parts. It seems odd that this just randomly started with no obvious cause in my eyes.

Cheers guys.

PS. My Pc Specs are as follows

CROSSHAIR V FORMULA-Z
AMD FX-9590 With Corsair Hydro H100i
Corsair Vengeance DDR3 2400mHz 8GB x2 (Total of 16GB)
AMD R9 290x with Corsair Hydro H50 (can't remember the brand, but its the stock version of AMDs design, I'll post the brand later)
Samsung 840 240GB SSD
Samsung 1TB 5400RPM HDD
Samsung 2TB 5400RPM HDD
Samsung DVD writer (Does anyone still use optical on frequent basis?)
x2 PCI-e x4 Firewire cards
x3 High Performance Corsair 140mm Fans
x2 Led High Performance Corsair 140mm Fans
All enclosed in a Corsair 760T case

 

[Vic 40]

With the H50 on the gpu is there something else,a fan,that is cooling the other parts of it? Tried playing with a table fan pointed at it with the case open? If you have one of these,at least try with the case open.

You can check voltages the next way if the motherboard is supported,

Download hwinfo32,

http://www.hwinfo.com/download32.html

You can open hwinfo32,after that open the sensor window by marking sensors only=V,
after that click run,then click at the bottom "Logging start" ,
after that choose a name and place for the log. like Hwinfolog at your desktop.Leave it open and do game/stresstest or whatever you do until a crash.The log will end at that point but will be saved.
After the restart upload the log to a site without to much crap (!),for instance dropbox,and leave a link to it here.
You could also look at the log yourself with either excel or libre office calc.

the rest is a possibility too.

Haven't checked for more info,but the motherboard has the latest bios?