To answer the questions regarding the specific manner in which the drives are failing, all of a sudden a reboot results in a computer that won't boot due "drive not found." The system works fine before the reboot. Diagnostics fail as well - the drive just isn't seen by the system. That said...
To shorten a very, very long story, we had a relatively new Dell business laptop's hard drive die early this year, so Dell sent us a new hard drive. This same thing happened four or five times over until they sent us a brand new computer in May. The same thing happened a few more times, and now...