+1 on HDD. Almost certainly a hard drive that was slowly failing and now, failed. Really the only way to diagnose this is to either use a bootable thumb drive, get another hard drive and install windows so you can see if the drive shows up in windows explorer, borrow or use a known good hard drive with windows installed on it or try the advanced boot menu options for a repair or recovery by doing this:
Read this page beginning to end prior to attempting safe mode so you are familiar with how it works. It's more difficult than it used to be in windows 7 and prior versions but still available. Also, when they say "mash" they mean like, as soon as you power the computer on immediately hold down the shift key and start repeatedly hitting...