Computer freezes after around 24 hours of use. Where do I begin?

Specs.
i7-2600K @ not OC'd at the moment to hunt for the problem
16GB RAM
980Ti GTX SC
Latest Nvidia graphics card driver.
Windows 10 Pro 64bit

Issue

• Computer just freezes after about 24 hours of use. It's not definite. Sound stops, graphic just freezes. Computer, I believe, is frozen. No BSOD or error appears even after the freeze.
• Event Logs reveal nothing. All it says is the computer was unexpectedly restarted. This is because I have to press reset (restart) switch to get out of the freeze.

The computer ran fine for years without a problem. Last time it was upgraded was right when 980 TI GTX came out, so it's been more than a year when it worked fine after the last upgrade.

I even went further and overclocked 0.1GHz higher than my original OC settings (4.5GHz) which it failed stress test, but it fails with BSOD (CLOCK_WATCHDOG_TIMEOUT) so the symptoms are definitely not similar.

It definitely seems to be happening often while playing games, I think. Although I did experience it time to time when I had a media player running (but it was paused for hours).

I really wish I could get you guys more info, but I don't have much.
If you ask for more so you could help me, I would do everything in my power to get you more information.

If you are overclocking stuff then you can expect such things to happen, things run hotter and component lifetimes are shortened, components go out of spec and so on. That old processor may well have had it's life shortened, so even going back to design speeds may not work.
We have no idea of the entirety of what you have done.
I would suggest you don't overclock anything, get back to basics, monitor temperatures to see whether they are within sensible limits with the CPU, GPU, then see how it runs with some stress test.
However some component(s) may have been permanently damaged.

Have you tried cleaning the computer? You may have dust inside causing it to over heat.

It might be the graphics card cooling tim too, they do dry out. Same for cpu. Same for Mobo mosfets.
First I would blow out all dust, try gaming w/o oc and see.
If it still happens, every component needs to be checked, reseated ........yadi,yadi yadi
Also check voltage rails on power suppy

Overclocking is always going to be the likely culprit when you run into system instability. We really cannot rule it out despite past stability, it just isn't a supported configuration.

Barring reverting to defaults for your processor, let's see what Reliability Monitor has to offer. If something is freezing your computer (that isn't overclocking) it may be generating event logs, and reliability monitor will help you see what's going on.

Overclocking does cause problems which is why I stated in the original post that I have reverted the configuration to default. The crash still happens without overclocking.

However, I think this freeze may have to do with an odd configuration I have with my graphics card.

My main monitor is running at 144Hz, but the secondary monitor (which is set to duplicate) is running at 60Hz. According to my research, due to a Windows 10 bug that's been around since its release, I cannot run the first monitor at 144Hz and the second monitor at 60Hz.
I somehow got that working (but Windows says my first monitor is running at 60Hz, I can definitely tell it's 144Hz). This somehow may have to do with the freeze?

I doubt this will ever be fixed by Microsoft or Nvidia.
Anyone got ideas?