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-D3VPTWindows 8.1 N(Core)6NPQ8-PK64X-W4WMM-MF84V-RGB89Windows 8.1 (Core) SLY9NXP-XT8MV-PT9TG-97CT3-9D6TCWindows 8.1 ProXHQ8N-C3MCJ-RQXB6-WCHYG-C9WKBWindows 8.1 Pro NJRBBN-4Q997-H4RM2-H3B7W-Q68KCWindows 8.1 Pro w/ Media CenterGBFNG-2X3TC-8R27F-RMKYB-JK7QTIf yo  ...