Dead hard drive

Not knowing which model you have and you've apparently determined the hard drive is dead the first thing to do would be to replace the drive then reinstall your OS. Hopefully you've been making backups with Time Machine to recover your data.

There are three possibilities here:

1. Within Disk Utility for macOS 10.13+ you may need to click "View" and select "Show All Devices" before the physical drive appears on the left pane of Disk Utility. If the physical drive is not seen, then it will be one of the other two options. It should appear with the make & model such as "Apple HDD....", or maybe "Hitachi ...", or maybe even "HTS547550....".
2. The hard drive has failed
3. The internal hard drive SATA Cable has failed. The internal hard drive SATA Cable in the 13" model has an extremely high rate of failure.

Unfortunately both items #2 and #3 are equally likely. The best way to test things is by connecting the drive externally or to another computer. If the physical drive is seen with either of these two methods, then the internal hard drive SATA Cable is most likely the problem, although I would still want to verify the health of the hard drive for a system this old because there is a very good chance the drive is worn out or failing even if it is physically seen. You can check the health of the hard drive by using DriveDx on macOS, or by using GSmartControl on Windows (portable app version is available so no install is necessary). Post the complete health report here using the "Additional Text" icon which looks like a piece of paper. To connect the drive externally will require using a USB to SATA Adapter, drive dock, or enclosure.