Hi. I'm David, and I'm happy to help you.
Based on your description, the crash may have occurred due to the graphics card driver or something it depends on. This crash may have corrupted the driver itself or system files, which would explain the sudden loss of performance and the games not launching. I need to investigate further.
Please see if your computer created minidump files.
These files are in C:\Windows\Minidump.
(If you don't have a Minidump folder, check if it is in the plural Minidumps.)
Copy any files you have to your desktop and store them in a ZIP file. Then, upload the ZIP file to the cloud (OneDrive), choose to share it, and get the link.
Then, post the link to the ZIP file here so I can have a look.
Looking forward to your reply.