New good spec PC build running slow

[lij]

Hello, my PC was built 3-4 months ago but I only started to use it about 2-3 weeks ago. Until yesterday it was running very well but I've started getting noticeably lower fps on everything for seemingly no reason, overnight. ie: 600-800 fps average on a game to 100-200 fps average. I don't know what happened. Does anyone have a clue what could be wrong or is there a way to restore it to how it was when I first started using it? I don't care if I lose all my files, settings, etc. Can't find any malware and everything seems to be running normally. I can get specific part specs if needed but off the top of my head:

 

Zotac Nvidia GTX 1070 ti

Intel i5 8400 Processor

2x4GB HyperX DDR4 RAM

Newer ROG Motherboard (forget model)

Water cooled (forget model)

500GB SSD (only drive)

ViewSonic XG2402 144hz 1080p Monitor