It has probably happened yesterday when upgraded windows 10. Looked like regular security fixes and silver light update it did not take long to download or install but it took some time to restart PC and i remember commenting that i installed windows faster and was worried that something went wrong with update. When it finally restarted everything looked fine and i went on steam updated Elite Dangerous and played all night.
When i have turned on PC today i was greeted by some promo screen for Windows Creator witch was bit odd coz my router was off. I turned it on and checked for updates and if i remember it right it was only this "Feature update to Windows 10". This one took a long time to download and to install. First thing that i noticed something was wrong when i try to run windows defender GUI was broken and it took 30 sec to launch (i was running it from old shorcut on taskbar) so i went to Reliability Monitor to check what was actually installed and found out it was wiped out completely with no history also. Right after i found out my C:drive is in red and there is only 12,9GB free and it looks like i have new windows installation and Windows.old folder.
I am wondering is it safe to delete Windows.old folder and what if anything went wrong and why was there no warning bout windows reinstall and whats with wrong date on Windows.old folder date of creation. Computer is running fine but i am bit worried. This Windows 10 was upgraded from Win7 long time ago.