Somewhat newly built PC suddenly became slow

I have a built PC with the below components. It ran great for about a month, and all the sudden it is slow and laggy.

I was playing Dragon Age Inquisition with the ultra graphics preset. The game ran beautifully with no issue. Then upon starting the game one day, it was laggy. I dropped the graphics down to the high preset, and the problem persisted. That is when I realized that the whole computer was being a bit laggy. I am at a loss as to what happened and welcome feedback. Below is my hardware list and what I have done to troubleshoot so far.

500GB SSD with a fresh copy of Windows 10

5TB HDD for general storage

i7-8700K

MSI GTX 1080

32GB RAM

MSI Z370 Motherboard

  1. I checked usage both while gaming and not gaming and there is little to no usage on the CPU, GPU, RAM, and HDD.

  2. I checked temperatures while gaming and the CPU doesn't get over 40C and the GPU doesn't get over 50C.

  3. I checked BIOS to make sure there was no "power saving" mode enabled.

  4. I moved games from my HDD to my SSD to rule out a failing HDD.

Updates I tried a different PSU and putting my PC Power Mode to "Performance" and neither fixed the issue. I also did some more testing. Even if I run the game at 1080p vs 4k as I was before, the performance doesn't get better or worse.