FPS varies whenever I turn on my PC

[thespoofo]

Basically, my PC sometimes turns on and games run completely fine. For example, a new game like Kingdom Come Deliverance runs smooth 60fps on Medium normally, however whenever I restart or turn on my computer(after going bed for example) it sometimes has lower performance than before. In this instance, I would be getting around half of what I normally would get.

I have previously found bitcoin miners on my PC and have managed to delete them all, at least according to my two antivirus programs(AVAST and Malwarebytes).

I have no idea why some days I get normal performance, and sometimes I get half of what a normally get. Have around 200GB free on my HDD and 60GB free on my SSD. Windows is installed on SSD and games on HDD. Once again, I have a suspicion there may be some kind of miner hogging up my resources, but every time I go to check through Task manager, it runs perfectly fine.

Already done stuff:

• 
  Cleaning out dust from PC
  Checking for bottlenecking
  Updating drivers
  Scanning for viruses
  Looking through my SDD for any miners
  Messed with settings NVIDIA Control Panel

I should also probably mention that NVIDIA GeForce Experience fails to detect any games on my PC, and whenever I scan it fails.

Specs:

Intel i7-6700 3.4ghz(but for some reason runs on average 3.7ghz even though I didn't overclock it)
MSI GeForce GTX970 4GB
16GB RipJaws Ram(Can't remember what Series)
Z170A Gaming M5 Motherboard
Cooler Master V650 Semi-Modular 80+ Gold Power Supply
Maelstrom 120 Liquid CPU Cooler
1 Case Fan+CPU Cooler Fan and the two GPU fans.

I cannot game currently with the state of this issue, I rarely get times when my PC is running normally. Majority of the time I turn it on it runs games on half what I usually get.

Thanks

 

[Lutfij]

1| Since you're on Windows 10, see if a repair install changes anything for you.
2| You may want to uninstall and reinstall Nvidia's Geforce experience, considering it's common for it to not find any games at random times.
3| Does the issue crop up when you're idling?
4| You might also want to see what Windows resource monitor shows up when you're idling. If near 100% then you're either suffering from memory leak or you might have a stow away.

5| Make sure your motherboard BIOS is up to date as well.