What you're describing is whether the BIOS is always being zeroed out, or the battery is dead, causing the BIOS to be zeroed out.
Many AMI motherboards, if you change the BIOS settings, will often not find which hard disk to boot.
Of course, there are exceptions. What often happens is that the floppy drive is somehow opened, and then it takes over the boot. So, the hard disk is not found.