The speed and frame rate issues seen in the above video are happening in every game I play, in exactly the same way. If I get into a game quickly enough after booting it will run smoothly for approximately 10-20 minutes. Once the issues start, they continue to worsen the longer I try to play. I've tried Judgment through Steam, Alan Wake Remastered through Epic, even flippin' Human Fall Flat through Gamepass. Games I've been able to run at decent settings for *years* are suddenly unstable overnight, even at the lowest possible graphics settings.

I've rebooted, I've air dusted, I've freed up space on both my C and D drives (both SSDs), I've run disk cleanup, I've run a full scan with Microsoft Defender, I've even run Windows Memory Diagnostic and saw no errors. I've run my games with one eye on task manager and every performance metric appears normal, nothing anywhere near 100% usage and GPU temps in the 60's and 70's during active gameplay, peaking at 81c for half a second one time. I've googled, acted, and tested pretty much everything short of pulling my BIOs battery (which Google assures me won't help but I'm *this* close to trying it anyways) or doing a complete factory reset. Maybe I'm missing something obvious, I'm not yet at the 'build my own rig' competency. Any advice or help would be appreciated.

Intel Core i9-7900X 3.30GHz  
NVIDIA GeForce RTX 2080 (8 GB)  
32 GB RAM across four 8GB cards  
2 1T-SSD internal  
Windows 10 Pro (not activated - never possessed a product key)

Computer was not store built, but neither built by me. I got it secondhand from a friend and don't know how old any given components are other than the PSU, which I replaced a few months ago attempting to repair a completely separate issue.

Performance issued overnight, at a complete loss