+1 here. I am betting your PS is jacked up. Ive seen this happen in friend's systems.
You can test all lines with a multi-meter but its probably just easier to get a different PS. Dont skimp on the cost, its one of the few things that will really keep your system working well.
I had one that was going bad and the "sleep" functionality stopped working correctly on my system and would do odd stuff. Replaced the power supply (and nothing else) everything is back to normal. Thats on my old i7 rig and was years ago. System is still going strong.
A multimeter might report the voltage is correct, but under load it may still drop
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