Probably harddisk died on you.

try removing the back panel and remove the harddisk and re-insert it.

if not remove the harddisk and put it into a external hdd case and plug it into other computer and see if the hdd is still fine.

There will be no data loss at all. Just put it into a external case and use it as a external hdd and backup your files.

If the harddisk is really damage, you wouldnt be able to read it at all. Meaning you'll lose all your data.

Harddisk currently is quite pricey. You can check in Garage Sales.