There are many things that can stop your computer running.
Not all of them result in your data being lost.

When your computer crashes or is disabled in some way by a virus or other annoying program it doesn't mean that all your information, photo's, music, video's go with it. The information you have stored on the hard drive is usually still there. You just need another way to access it.

Physically removing the hard drive and connecting it to a working computer is often all that is required to retrieve your information. Reinstalling the operating system and copying your data back to your original system completes the process.

The rare occasion is if the hard drive itself is what fails. Even then it is possible to retrieve the information you have stored but not many people would consider the cost worthwhile.