The most common reason for a rig on any OS to crash completely is the used overclock profile. Unfortunately setting it up is a classic example of being easy to start but hard to master — and even then, there is a factor of silicon lottery, which makes it impossible to simply copy the best settings found for one card over to the other of the same model, as the actual physical chip is a bit different, the specific cooler may contact the system a bit better, etc., etc.
When the configured OC is unstable, the card may lose the connection to the driver and resources interacting with driver or card may hang or crash completely, which in some cases can trigger a restart, BSOD, etc.
You can read more about configuring the overclock here.
-driver and its settings
The other factor which plays a very important role is hardware. This includes all the components used in the system and BIOS settings.
The likeliest troublemakers are risers and the power cables used to run them — you should always power risers via PCI-E 6-pin connection instead of SATA or MOLEX as both SATA and MOLEX are not guaranteed to provide the power that might be needed by the cards in the system. Still, a riser might be a cause for reboots, hardware being not detected or producing errors. It often helps to set PCI-E to Gen 2 in the BIOS of the system in order to prevent excessive stress for the risers.
The other part of the hardware that is most critical for the well-being of the system is the Power Supply Unit as with a good-quality but not big enough PSU the system will shutdown to prevent damage, and with lower quality power supplies, it may outright damage the components. Read this article on how to choose a good power supply (or multiple).
Another one is the GPUs used in the system. Some degrade and would require different clocks after years of mining, others might have issues with fans and overheat as a result of it, and some of the cards can break. If they do, it might not work at all, or be not recognized by the driver, or crash the system as soon as any load is applied to it. It's necessary to take good care of the hardware in your system — i.e. dusting the cards regularly, in several years time a thermal paste replacement might be needed, and in case of Nvidia's 3000-series GPUs, generation of which is also known as Ampere, a thermal pads replacement is recommended for day 1, especifally for RTX 3090 cards.
-Screen saver (part of power settings kinda)
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