A computer's hard drive may have a MTBF rating of over ten milion hours, which basically means that on average, a computer's hard drive should not fail in one's lifetime.  However, as with anything man made, the hard drive can fail at any point in time and sometimes for no apparent reason.  Should this happen all pictures, financial information, and other data and programs will be gone.  So be prepared by having a data recovery plan in place.  Article "Importance of Backups" talks about serveral stategies you can take to minimize data loss should your computer's hard drive fail.