If you have black screen and you can see your mouse cursor do this (how i fixed it):
when booting keep pressing F8 and it will ask you if you want to go into advanced options or restart (or shutdown PC), you go to advanced options and click system restore. Choose one of the dates (i'd recommend the earliest one) and wait for it to restore it. I lost my data (i don't know how) on C drive but i got it fixed.