Sudden computer restarts(already replaced PSU)

Question

So, this computer problem has been driving me crazy for the last year or so: every so often while gaming(if I game intensely for ~10 hours it happens once or twice), usually on the parts that seem more intense computationally(not 100% confirmed it's this though), my computer just restarts. On restart my sound card is not detected by Windows(it has lights on it which are on though), and I have to shut down my computer and wait for ~3 minutes to start it for it to work again. Eventviewer in Windows only shows something about an unexpected loss of power.

Stuff I've tried to fix this issue

• Swap around some of my USB peripherals, use other ports etc.
• Check temperatures of cpu/gpu/disks to see if anything was overheating, nothing was.
• When the problem started it gradually got worse, at first my entire computer wouldn't start anymore for the duration it now takes me to wait for my sound card to work again, and eventually it didn't matter how long I waited: my computer just didn't start anymore. I then tested starting my computer by basically re-assembling it and trying it with a strip of RAM less, only onboard graphics card etc. to debug what was causing the problem. In the end it started when I didn't have my graphics card in it, so I replaced that. This fixed the problem for a while.
• Problem came back(including not being able to start pc at all), so after some more debugging I replaced the PSU(got a new one that's kind of overkill power-wise). And I replaced my power strip at the same time since it was getting old and I didn't want to break my new PSU with some power strip problem. This fixed the problem for a while.
• Now the problem came back again, I already checked temperatures again and nothing seems wrong. It's not as bad as before, I can still start my pc after a crash, but I fear it'll get worse again.
• Not sure when I tried this one, so I put it at the end: I tried playing without my sound card for a while, the problem still occurred so I just put it back in when I replaced my PSU.

My Specs

(nothing overclocked)
CPU: Intel core i7 4770k
Graphics Card: Nvidia GeForce GTX 980
OS: Windows 10
RAM: 16GB
PSU: Corsair RM750
Motherboard: MSI Z87-G45 Gaming
Soundcard: Soundblaster Z

My Suspicions

Because there is nothing in the logs and it's very hard to reproduce this reliably(sometimes it just doesn't happen for a few days in a row) I don't have a lot of suspicions. Because my soundcard isn't recognized on startup after a crash the only lead I have is that it's something in that. I highly doubt it's in my PSU since I replaced that already, same goes for my graphics card.

Any ideas or fixes would be hugely appreciated, since I'm out of ideas here.

EDIT: "restart" might have been a bad choice of words, it's more like pressing the reset button, so it just instantly shuts down and then starts again.