PC Reboots Only While in Game

[Servostopper]

SUMMARY
My home PC has began rebooting abruptly during games. I have had this particular setup running for over a year, and up until last week I had never encountered these symptoms. I have not encountered these power restarts outside of gaming. Below are my system specifications.

Here is a link to a 1m long video monitoring the voltages, temps, and other diagnostics of my CPU and GPU before a reboot in game. Note: the PC was on for several hours before this, where I was watching videos and have no such reboots (PC reboots at the end of the video): https://goo.gl/nTqYFc

SPECS
CPU - Intel Core i5-2500K @ 3.30GHz 3.60 GHz
MOTHERBOARD - Gigabyte GAZ68XUD3HB3
RAM - 4GB(x4) Kingston HyperX Genesis DDR3 1600MHz
GPU - EVGA GeForce GTX 980 Ti
PSU - Corsair HXi HX850i
HEAT SINK/COOLING - Swiftech H220-X
CASE - AeroCool StrikeX-AIR

ADDITIONAL TROUBLESHOOTING NOTES
- The restarts are without a BSOD.
- I have not overclocked any of my components.
- My in game temps are: CPU <= 45 deg C & GPU <= 45 deg C.
- Event Viewer shows the following error [Kernel-Power 41 (63) error: The system has rebooted without cleanly shutting down first. This error could be caused if the system stopped responding, crashed, or lost power unexpectedly.]
- The reboots have been varied in multiple games (HotS & PUBG), both in game and when idle in menus. 
- The restarts have started happening sooner into the games running.
- There haven't been any recent driver (as far as I know of) & OS updates.
- The issues started (a couple hours) after I coincidentally cleaned up my desktop and updated the package of Spybot Search & Destroy on my PC. I highly doubt either of these are responsible, but including this to be thorough, who knows.
- I also swapped out the old surge protector I have used for a long time, in the hopes of that fixing the issue - it did not.

FINAL COMMENTS / UPDATE

I started off by thinking the PSU was the problem. I got a new PSU (a AXI860i, I left the original cabling in - although I doubt that made a difference) and swapped it in. The system started up fine and I downloaded a few system updates. A few minutes later I launched a game as a load test. After a minute the system turned off. Not a restart this time, my PC won't turn back on again. I unplugged everything, and began inspecting. Unfortunately, I was greeted by the smell of burning coming from the top of my GPU - which I think may have had it's life cut tragically short. At this point I think I will need a new MB, and GPU. 

 

Are there any suggestions here for what I may test or if I have missed something obvious.
Any comments are appreciated.

[Taswell]

I think your gpu was shorting out the pci-e lane and the motherboard shutoff to protect itself. the motherboard might be fine, gpu not so much  

[Servostopper]

2 minutes ago, ITheSpazI said:

I think your gpu was shorting out the pci-e lane and the motherboard shutoff to protect itself. the motherboard might be fine, gpu not so much  

Would that explain not being able to start the system up again? Is it worthwhile/safe to take out the GPU and turn the system on OR subject a new GPU onto this motherboard?

[Taswell]

1 minute ago, Servostopper said:

Would that explain not being able to start the system up again? Is it worthwhile/safe to take out the GPU and turn the system on OR subject a new GPU onto this motherboard?

I would unplug everything you dont to hurt and see if you can get it to post with no gpu, if not then i guess you do need a new motherboard but i don't really know how it would've died, unless the gpu screw it that hard

[Jurrunio]

At first I think it's the CPU degrading over time and is no longer stable at its current voltage because PC reboots during heavy load is common for unstable overclocks, in which raising voltage helps.

 

However you mentioned 'burning smell', so I guess capacitor(s) on the mobo or graphics card going out. In this case I think it's more likely to be the mobo becuase it's older.

[Madusha]

I had this issue a while ago before I upgraded, I went and dusted the pc out to see if anything was disconnecting and it seemed to fix the issue, I believe it is the either the PSU not delivering enough power to the GPU or the GPU itself acting up.