It seems the advice is either reset PC or a fresh install.
both require reinstalling almost everything again. But you can save a lot of files doing this: http://www.howtogeek.com/howto/windows-vista/use-ubuntu-live-cd-to-backup-files-from-your-dead-windows-computer/ or putting hdd into another PC and copying data over.
On another PC, download the
Windows 10 media creation tool and use it to make a win 10 installer on USB
Reset:
change boot order so USB is first, hdd second
boot from installer
on screen after languages, choose repair this pc, not install.
Choose Reset
Choose Keep files/Settings as this will keep library folders (documents, pictures, music, movies) and Logon info
PC will restart and install win 10 again.
Fresh install:
change boot order so USB is first, hdd second
boot from installer
follow this:
http://www.tenforums.com/tutorials/1950-windows-10-clean-install.html
A fresh install would likely install the update that caused PC to roll back, but if you hadn't fresh installed and had previously upgraded from win 7 or 8, then chances are this second upgrade was too much for win 10 to cope with. I expect you were getting the Anniversary Update that was released a month ago