I'd move to the next step. Which is heatsink compound replacement. After a few years it can get old and crack so like a 50,000 mile car service you get in there and change all heatsink compounds then check fans on the final checkout.
Not sure where to start but I guess specs would be useful.
Specs:
Motherboard: MSI Z270 Tomahawk
CPU: i7 7700k
CPU Cooler: Corsair H50
RAM: HyperX Fury 16GB DDR4 2133 (2x8GB)
GPU: PNY GeForce GTX 980ti reference model
Storage: SSD - Crucial MX200 2.5" 250GB internal solid state drive
HDD - Seagate barracuda 2TB 7200rpm
PSU: Corsair 750M
Issue: So my PC was working perfect fine and normal. All of a sudden I started getting issues where all my monitors (3) would go black and then come back on. So I instantly figured I had a problem with my GPU. Then the issue escalated further. My PC would be on for no longer than an hour and all my screens would go black then the pc would shut down and practically restart itself except for I would notice that my GPU would not turn on with the rest of the pc. I tried taking it out and blowing the dust out of the gpu with canned air and put it back. It worked for a good day before my pc completely died. The same issue happened again where it restarted itself only with the GPU not powering up. So I took it out tried cleaning it changing pcie slots. Nothing worked. Then I realize when I was trying to turn on my pc other stuff started breaking too. My case fans wouldn't turn power on and neither would my CPU radiator fan. But the mystic lighting on the MSI Z270 Tomahawk would light up and it seems like the motherboard would be fine. Now I can't figure out what the issue is. I don't know if it's the GPU and I don't have another pc to test it in. I'm not sure if my PSU is dying and maybe not outputting enough power. I'm not sure if there's an issue with my motherboard because the case fans won't work anymore. Any help or suggestions is appreciated. Thank you.

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