One day you turn on your Windows Vista PC, and it gives you the dreaded "BOOTMGR is missing. Press Ctrl+Alt+Del to restart" message, in menacing white font on black screen. So you hit Ctrl+Alt+Del ...
That should be another way to fix the boot order... If the bios changed the bootorder (which happens some times after a disconnect/reconnect), it would be trying to load bootmgr from the drive that ...