Comp Randomly slow and laggy, please help!

[Fentech]

The other day when I walked back to my computer from lunch it had a few warnings that programs had crashed, so I restarted my computer. And, ever since, my comp has been very laggy with every event, whether it be opening an app, looking at all apps in the start menu, loading a web page or playing a game etc. It's hard to describe but it's a mix between system lag and what seems like frame rate drops.

Anyways this is everything I've tried thus far to fix the problem:
- Ran a full virus scan with Windows Defender which came up with nothing
- Ran Memtest86 all night which came up with 0 errors
- Checked device manager and says all components are running properly
- Stress tested CPU which went just fine
- CPU temp is between 29 C and 32 C
- I updated video, chipset, audio and hardware drivers
- Cleaned registry
- Ran Ccleaner
- Ran system file checker
- I have 2 sticks of RAM so I tried running 1 at a time in different slots on the motherboard to no avail
- I installed CrystalDiskInfo to check S.M.A.R.T. info on my SSD which turned up fine

I have no idea what this could be. This timed up with nothing, no windows update, no new install, nothing. If anybody has any leads, I am all ears.

Here is my system:
Windows 10 Home 64-bit
Intel Core i7 4770 @ 3.40GHz
8GB DDR3
MSI Z87-G45 Gaming Motherboard
2GB Nvidia GeForce GTX 760
500GB Samsung SSD 850 EVO
1TB Seagate HDD

 

[Dark Lord of Tech]

Reinstalling windows 10 usually cures this type of issue.