HDD does not appear - is boot order incorrect, or has HDD now completely failed?

My computer has a HDD with a very large number of bad sectors. Currently I am running Linux Mint Cinnamon Victoria as a Live DVD from the DVD drive, so it is running entirely in memory.

I had disconnected and removed other secondary HDDs that did not have any OS on them, but that has made the boot order change all by itself.

The problem is that the HDD does not appear anywhere. It does not appear in Disks, etc.

The desktop computer case and motherboard are both OEM.

Is the boot order wrong in what used to be called BIOS but is now called UEFI please?

The current boot order in the American Machines Aptio is:

1. P1: TSSTcorp CDDVDW SH-224DB

2. UEFI OS (PO: ST31000524AS)

3. PO: ST31000524AS

4. Ubuntu (PO: ST31000524AS)

5. UEFI: TSSTcorp CDDVDW SH-224DB

I do not know what the above means, or how it knows I've been using Linux. The DVD drive has to be first so that I can run a Live DVD.

Question: do I need to change the boot order, or has the HDD now completely and definitely failed?

Thanks.

(There was another Solved thread about the failing HDD under Linux Mint.)