Computer tech question:

No boots, random reboots, blue screens, loud & weird noises, smells and sparks are a few symptoms of a dying PSU. But a lot can be similar with other hardware failure. Hardware or software is probably the first thing to figure out. Have you recently upgraded any part of it? The excess draw could cause it to give up. And are you making the switch to Windows 10 anyway when it launches at the end of this month? I am going to it and it rules the software out anyway if you are making the change.

I had a PSU that was maxed out in my old build that would shutdown when going to full load, if it didn't it would be fine all night. But the first big pull when a game fires up would either shut me down or be fine. Happened when I logged into TSW, I was fine until the game first came on. I would usually get a hello out to the Cabal and then go offline lol. If it is up to the PSU's max you could pull the GPU and use onboard if applicable and see if the power drop helps things out. Memory failure can also cause random problems, if using dual sticks you could possibly pull one at a time.

It could be the HDD failing too on the hardware side. Without bits to swap out its hard to solve the problem really.

I guess the cheapest option is a full re-install, sometimes welcome anyway for general speed up. But a pain in the butt re-installing and setting up all accounts etc again. I bought a decent Antec PSU this time, a part of the system you really shouldn't cheap on but something I am guilty of often. Really as well it is nearly the only part that you move over to a new system build as well.

The fan speed changing could be a setting but unlikely on case fans, which could be a sign the 12v is fluctuating which in turn may be causing your GPU to throw a wobbler.

I also think it can be the PSU, it may be time for a new one...
You also need to calculate the WATT usage vs PSU output...

I wouldn't think you would have to under volt with the Hyper on there, I use that too and my i5-2500k is running around 4.3 ghz OC at not much more than 60 degrees in Prime, I think I fell lucky with the "golden child" of chips though. I took it to 5ghz comfortably on air but played safe. That and the MB is all I didn't upgrade entirely due to OS licenses. But I don't think it should be going above 75, I am personally happy in the 60's but low. I wouldn't expect an i7-950 to be any higher than 65 degrees stock with the Hyper. But you can fall unlucky with a bad one I guess.

Did your undervolt survive a decent length Prime or Intel Burn test? I guess all electronic devices lose efficiency and will draw more as they age. It would potentially be my first port of call but I wouldn't be ruling out the PSU either. I would return it to stock or marginally increase it especially if you haven't tested it since installing the Hyper. I intended on going water in my build and used the Hyper as a budget option to get running, I have been nothing but impressed. I put another fan on as a push pull setup. I got a Corsair Air 540 this time as a case, the thing is huge/quiet and cable management like I have never seen. Your ambient temps are high but then I live in Yorkshire in England lol, we see no heat only rain clouds.

I wouldn't expect a Corsair PSU to fail in such a short time, but then all electronics can. Its probable "actual" output won't be so bad either. There are a lot of memory sticks that could go wayward there though, I haven't looked into how "final" a memtest could be though. You certainly have enough to sacrifice some though if all else fails.

You can probably rule out software then with a fresh install giving issues.

CPU temp? That's a bit high imo...

I wouldn't bother much with flashing the bios btw. Unless there's something specific you really need from the new firmware. I never upgrade my motherboard's firmware unless I have a reason to.

can you upload a pic of the BSOD ?

I'm in attic and my room temperature in summer is literally hell... sometimes it gets to 40-45ºC. My CPU temperature is about 10-15ºC when idle and 40-50ºC under load. It can get to 70ºC when running specific programs designed to stress the CPU, but never under normal load.

I hope you get it all sorted mate, it frustrates the hell out of me and I have several computers in the house to swap parts about. With the latest build I had no display what so ever and suspected the new GPU was bad. Swapped out part after part trying to narrow it down only to discover, the idiot that I am, forget to plug in the 8 pin connector from the PSU to the CPU. Wasted hours..

And now I have wasted money too. I had a 3x21" monitor setup from the last computer, but then opted for a wall mounted arm arrangement to clean the build up a bit instead of 3 stands. Didn't like it at all, came too far forward. That is now in the loft. Then I decided I wanted a larger 27" monitor above the 3 to use for gaming and video stuff. I have installed that today and now the address bar is over 45 degree high on looking angle. It isn't comfortable. So 2 more stands are now ordered and I am after copying number 12 on the link below, as long as the overall heights match I think it looks ok and functional! I think that is a good compromise. I don't really game in Eyefinity but I couldn't be without multiple screens for all other duties.

twistedsifter.com/2012/06/amazing-computer-station-multi-monitor-setups/

I have a CORSAIR RM850 (850W), it is awesome !!!