Hi itshugh and welcome.

Windows 8 notebooks will not carry the usual COA sticker.  The Activation process has changed fundamentally with Windows 8.

Previously, OEM machines were shipped from the factory already activated.  Now ALL computers will need to be activated on first use and there is no longer any periods of grace etc.

The individual product keys are supplied by Microsoft and injected onto the motherboard of each machine during manufacture - so it is now impossible to use the Key on another machine. Activation is automatic - although manual activation is possible in the unusual case of difficulty by providing the Activation Center with a very complicated code which will be supplied by the firmware on the motherboard.

This means that you can reinstall Windows 8 from ANY media and be automatically activated.  Replacement of HDD should not be a problem but, of course, a problem will exist if you change the motherboard!