All computers and their components are subject to failure. In fact sooner or later every business will be confronted with some type of computer malfunction.
The largest threat to businesses during a failure will be data loss. Most people, and--sadly enough--most businesses only react to disaster after the damage has already occurred.
Even though data recovery technology has improved, the cost from an economic point of view can be quite expensive with no guarantee of success. It's always a wise decision to protect yourself against data loss.
The best protection method is to backup your important files, not just when you feel like it but on a regular basis. Simply put, backup means keeping a second copy of anything of importance and storing those files in a location which is relatively safe from hazards like unexpected power failure, hard disk failure, virus/spyware attacks and theft.
So what data should be backed up? The simple answer is any file that you would miss if you didn't have it. This includes documents, presentations, spreadsheets, accounting data, tax returns, calendars, telephone directories, photographs, music, saved web sites, passwords, sent and received emails, etc.