SpookyCitrus

Looks good, only thing I would change is ditching the two mechanical HDDs for SSDs and doing an Nvme SSD instead of the Sata for the boot drive. If it's just for gaming there is literally no point in putting mechanical HDDs in the computer. Do a 1TB or 2TB Nvme SSD for your boot drive and then a 4TB Sata SSD for your storage drive.

Those are normal temperatures, so it's likely not a thermal issue. The GPU will not show temps in BIOS, only in Windows.

Standard superglue and careful application should be all you need. Don't use a lot and only get it on the heat spreader and plastic RGB diffuser. You can get a gel style superglue as well so it's less runny and will stay in place.

Just to reiterate, jumping the power supply won't do anything for you. It's strictly a test to see if the power supply works by turning it on. Yours is, it's not a test for figuring out why the computer turns off. You'll also want to make sure the power supply is outside of the case and or unplugged from everything if you do the jumper test. If it is a thermal cutoff it's going to be CPU or GPU, it should show what temps your CPU is running at while you are in bios. If you can see that metric, what is the temp while in bios?

@eerie5 Is there a reason why you want/need the ability to use floppy disks/cassette deck? Such old hardware isn't used anymore and most floppy drives are going to be expired or inoperable anyway. Do you have like an old stock pile or it it just something you want to tinker with? Most of the older interfaces out there have USB adapters so depending on what you're trying to do that might be a cheaper/easier option.

If this is DDR5, 2x32GB for sure. DDR5 memory controllers have a hard time running quad module kits. Dual channel is better for DDR5 anyway.

The only way to test the power supply itself would be to use a PSU Tester(inexpensive on Amazon) or trying a different power supply in the system and seeing if it still has the some problem. There is a home test using a paperclip to jump the power supply but that is only to see if the fan spins up and it powers on. In your situation you would need to know if it is supplying the proper amount of power per connector.

If it's doing all of this in bios as well, that rules out software. It's most likely one of three issues. Typically this would be either the Power Supply, Ram, or Motherboard. In order to troubleshoot and figure out which one you would need to test new or known working parts in the system, if you have hardware troubleshooting experience as well as the necessary parts handy, great, I can recommend you what to test next. If not and it would be difficult for you to get the parts needed for testing I'd recommend taking it into a shop or professional.

Yeah, that's likely a cable/adapter issue, I'd make sure they're all gigabit cables. Also another option would be to use a powerline adapter set if you have to use ethernet. Otherwise, if your WiFi is able to deliver your system it's full speeds, just use that.

When it "dies" is it just turning off? When it does, does it stay off? Or does it turn back on, on it's own? Sounds like a faulty power supply or other hardware issue. What are your full system specs? Also does it freeze when in bios? Or only when in Windows?

Are these wireless or wired mice? When you're plugging them in are you using the same USB port every time? If so I'd try a different USB port if possible.

Only option for drivers is to use DDU to remove the old ones and then install the newest available for your card. Nvidia should still have the drivers available but keep in mind they're going to be a few years old as the 600 series cards haven't been supported in quite awhile. If that doesn't work it could be your cable, if you have another one handy I'd try that. But with a card this old, you're most likely looking at failure. If the drivers or cable don't work I'd look into replacing that GPU.

Those drives are usually pretty solid, when you tested your Ram what program did you use?

You can use internet recovery, a program such as Mint to make an install USB for MacOS(you can also do this with an installer download), similar to making one for Linux or Windows. As long as you have a compatible version of the OS that is supported by the Mac in question. You'll need to either install the MacOS version that originally came on the Mac or one that is still supported by it. Apple cuts support for certain Macs so that they won't work with newer versions of MacOS. You can figure out the latest supported version your Mac will work with by looking up the serial number on everymac.com

If your ram is good and it's not software because you did a complete fresh install, the only other cause for these issues would be a problem with your storage drive. What make and model 4TB nvme do you have, and is it your only drive?