What's gone wrong with my storage device?

There is a myriad of reasons for which a storage device may not be accessible, so let's try and separate them into broad categories before we get into the detail of what can be done.

There are fundamentally four layers to the operation of a computer:

The hardware - This is the physical computer, including a processor, memory, input/output devices (display, keyboard, mouse, etc.) and storage (floppy, optical - CD/DVD, hard disks, etc.) devices.

The Operating System - Windows, Mac OS, Linux, etc - This is basically an abstraction layer providing a clearly defined set of services (open a window, access a file, etc.) to the Applications layer above it. It uses device drivers to translate the interaction between the operating system and the device itself.

The Application - That's the program that you are running to create your piece of work - your document. Applications are rarely a source of problems (bugs). What happens more often is either an incompatibility (particularly with the version of Operating System used) or an interference (particularly from device drivers or corrupted preference files).

The Document - Again, problems here are relatively rare. Document damage is most often due to malfunctions further down the chain that have resulted in garbage having been included in the document. System crashes and compatibility issues are most often the culprits.

The first point to keep in  mind is that each layer can impact on the layers above it but not the other way around. So one can do some simple testing to pinpoint the real source of the problem. Unfortunately, operating system messages can be misleading in those circumstances. They are not incorrect but only tell you the last step of the mishap, not its sequence.