It means in plain english that your PC is trying to boot from a hard drive that does not have a bootable source (OS) on it. Either its failed or ths OS is corrupt or its a new drive which is not formatted.
From your intro i get the view that this is your original HDD that you have had for some time - to confirm its failed try and see if it is identified (Primary master I expect) in BIOS when you first switch it on.
Before you can it one thought - it might just be wort rejumpering it to a slave and seeing if it is recognised in that configuration. This happened to me I had a drive which would not function as a master but would as a slave I am still using it as secondary storage. Worth a try.