No bootable device- insert boot disk

[Ella2505]

I have turned my computer on today and a message saying something along the lines of “boot image not authenticated” so I have tried to do a hard reset; nothing. My screen does not change from no bootable device.
How can I fix this?

[Huffer]

We need the model number of the laptop so we know what tools are built in but if it is less than about 5 years old you have a very good built in hardware diagnostic capability. Tap esc as you power on then F2 when the menu appears...look for component tests/storage and run the full test on the hard drive and report back what you find out, please. 

[Ella2505]

I have run a hard ware test. And the short DST has failed. I do not understand what this means

[Huffer · Accepted solution]

The hard drive needs replacement. We need your model number to provide specific help for replacement instructions and the type of hard drive you need to buy. We have helped hudreds of people with DIY hard drive replacement over the years. 

Very likely not as expensive or difficult as you fear. 

[Ella2505]

Thank you for your help.