Get the mobo manual out and read it; the answers are in there (RTFM). if you dont have it, go download the pdf version from the mobo support page (on your mobile - as your PC isnt working).
Possible causes in order of likeliness.
You did something.
Malware.
Botched software update (usually M$).
Failed HDD.
Bad SATA connection/ SATA port failure