Windows started loading too long (black screen)

Feb 4, 2019
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Hello everyone.
Today I encountered an new error.
Basically, playing a game (Civ6) I got BSOD in Win 8.1. Never seen such thing running this pc.
Error was something like whea_uncorrectable_error.
I restarted my pc but Windows won't load up (black screen). I had disc with Win8.1 install files so I managed to repair my Windows from 10s or smth like take using windows RE environment. At first repair tool cannot even acces my drive but then somehow managed to repair it.
But now Window loading takes around 3-4 minutes (just black screen after BIOS is loaded) whereas before it took a few seconds. I wonder, why? Plus now I wonder whether I should have repaired it at all (cause all programs are gone, thanks files are ok) and just waited untill it loads.
My PC is i6700k, ASUS Z170-A, MSI GTX1070, SDD1TB Kingston.
 
Feb 4, 2019
2
0
10
Now it's getting even worse. Today I had 3 times(!) lag when my video driver stopped working! That's never been a case! Please, help. What can cause these issues?