From what you said at the start it sounds like the HDD has shat itself. An easy and cheap fix, though it can take a while to get everything loaded.
Big thing before you get going is to check the Microsoft Certificate of Authenticity (COA) to see it if is readable if Windows 7 and earlier. After that it is coded into the BIOS at factory and automatically picked up with the installation. Take a photo of the COA to make it easier to punch the numbers in, they always put it underneath which isn't the most helpful.
If you get stuck for a disk/USB pen drive with the operating system let me know.
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