First try Control-Alt-Delete to open the task Manager, click New task, then type CMD
in Run box.
In Command Prompt type slmgr -ipk
followed by a space and the Product ID, press Enter then slmgr -ato
to attempt activation. Reboot.
If that fails it could be non-geniune lockout caused by a drive letter change in registry which happens sometimes during reimaging or repartitioning.
Use FREE Rescue Kit Express | PARAGON Software Group
Boot the Paragon CD - select Normal Mode , then Boot Corrector.
Correct drive letters in the system registry.
Release the incorrect letter first, if necesssary.
If this fails you'll need to reimage this time selecting Auto for drive letter.