The message "Operating System not found" suggests that the Master File Table (MFT), if applicable, was corrupted. So the BIOS could not find where on the disk the OS lives.
Why did this happen? 1.) Planetary misalignment 2.) One of the Chakras was out of whack 3.) Flipping of the magnetic pole from North to South 4.) Random bit flipping 5.) Donald Trump's Tweets (why not?)
Take your pick.
Yes, this is a small attempt at humor.
Personally, I go with #4.
Since you deleted and replicated again, maybe a temporary condition.