Recently had an issue with my own laptop where Windows 8 wouldn’t activate. I was pretty sure the product key was wrong, but there isn’t any way in the GUI to change the product key like there was in Windows 7.
After some searching I found a MS article that explained how to change the product key in a few different ways.
Using the Slui.exe 0×3 from a Run dialog allowed me to change the key and successfully activate. Using the slgmgr.vbs /ipk would work as well, but the slui.exe was new to me so I used that method.
Hope this helps someone else that runs into the situation.