To (re)-install Windows 8 or 8.1 with retail or OEM media (including the online media creator), you can (temporarily) use the "generic" installation keys, officially provided by Microsoft.
These keys allow you to perform the installation, after which Windows will run in a 30-day trial mode, before a proper key and activation is required. The keys are language and platform-independent.
|Windows 8.1 (Core)||334NH-RXG76-64THK-C7CKG-D3VPT|
|Windows 8.1 N(Core)||6NPQ8-PK64X-W4WMM-MF84V-RGB89|
|Windows 8.1 (Core) SL||Y9NXP-XT8MV-PT9TG-97CT3-9D6TC|
|Windows 8.1 Pro||XHQ8N-C3MCJ-RQXB6-WCHYG-C9WKB|
|Windows 8.1 Pro N||JRBBN-4Q997-H4RM2-H3B7W-Q68KC|
|Windows 8.1 Pro w/ Media Center||GBFNG-2X3TC-8R27F-RMKYB-JK7QT|
If you have an official Windows 8 key, you will need to use the installation key to perform a clean install of Windows 8.1, then activate with your official key, because Windows 8 keys are not accepted directly in Windows 8.1 setup.