We all hope that it never happens, but the reality is that occasionally a computer will go down hard. The power may go out, and your UPS does not provide the protection that it should. Or, you may not have a UPS, which you really should.
Sometimes, the system just locks up, and the only option is to turn the power off, or disconnect it. Sometimes, someone shuts the power off without shutting down the computer, because they do not understand that it should be shutdown first.
Whatever the reason, taking a computer down hard runs the risk of corrupting files. While it is bad enough, it the quote you were working on gets corrupted, it is even worse if it is one of the operating system files.
Corrupting part of the operating system usually means that your system will not boot at all.
This is where you really need an expert. I have run into this situation many, many, times, and sometimes the fix is quick and easy. Many times, however, it takes some time to determine where the problem is, and what is needed to fix it.
There have been times that the problem was in a system log file, that could safely be cleared, and the system was back up and running in minutes. Other times, individual operating system programs had to be isolated as the problem, and replaced one-by-one. Rarely, the entire operating system has to be restored from backup. Once again, pointing out the importance of keeping backups current.
The best you can do, is make sure you have a good UPS, and keep your backups current. After that, if one of the other scenarios occurs, and you find yourself unable to boot your system, call on the experts.