Was helping my niece with the this problem on her laptop, tried all the methods mentioned and the one that worked was running malware scan and squashing 30+ bugs. Didn't bother to check which one was causing the problem. After that it went straight to log in screen, log in and started patching. Unfortunately, wasn't able to finish the patch cause I forgot to take the power cable -_- and so battery went poof...
So, try all the methods cause one might work for one but not the other.