I would like to know where I can get the instructions to do a complete reformat. If the problem is extreme enough, the program that is running doesn't know how to proceed. When that happens it causes the computer to stop in its tracks and you get a fatal error message. When the errors are really extreme, areas of memory are changed and become so confused that they can't go on. Error messages, mysterious and frightening as they can be, are usually not very serious.
Computers crash all the time.
Sometimes crashes are serious, but usually they are minor. In either case, you'll always get an error message. It's completely normal. Errors are usually caused by program changes or bugs. A problem in a program will cause a change in a memory area, which causes a crash.