PC Shut Off while playing a Game and Watching a Stream

I was playing Far Cry 4 on my first screen, while on my second stream, I had a twitch stream on. All of a sudden my PC turned off without warning. Now, it had done this before, and had turned on right away by itself, which I thought was an overheating issue, so I had my fan speed turned up, mostly the GPU fan. But this time, it didn't turn on again. I tried pressing the power button, but nothing happened. When I went to pick the case up so I could open it up, there was a metallic burning smell, which made me think that something had overheated. I took out the GPU and let it sit for a while because that's what I thought it was, as it seemed that's where the smell was coming from. After it cooled down, I put it back in and tried again. This time, when I pressed the power button, there was this hissing sound for a moment, and then nothing. The motherboard that I have has a little power button with a light on it, (I think it's the CMOS button but I'm not entirely sure I'm not that great with PC terminology) and the light for that is on, which leads me to believe that power is running through it. If it was the GPU as well, I'm pretty sure that the PC would at least turn on correct? My guess is that the PSU has burnt out or has failed in some way, but it could also be a CPU or a MOBO issue, as I have had problems with my MOBO before, although I don't think that it's the CPU because I have a fairly competent liquid cooling unit, and at full load, I don't even think the CPU temp hit the 60 degree range. My specs are below if anyone knows offhand if there are any specific issues like this with my particular hardware. Luckily I was already thinking about upgrading, but I was planning on trying to sell this to get some of my money back for it, and I can't sell a dead PC.

Specs: Intel Core i5 3770k running at 3.8 gHz
EVGA Geforce GTX 680 (I can't seem to remember what it's running at or how much memory is in it)
Gigabyte GA-Z77X-UD3H Motherboard
2x8gb HyperX Red RAM
Seagate 1TB HDD
Kingwin 1000w PSU (I think that's the wattage, it's been around 4 years since I built this PC so I can't quite remember everything, and it doesn't say it on the PSU itself).
I was also having problems with my MOBO USBs, so I ended up adding in a little Rosewill USB PCIe card as well, which sits right next to the GPU, a little closer than I would've liked it, but thats the only port that worked with my case.