HP Recovery disks normally include the OEM_SLP Key - so that should have worked.
Two possible causes
1) teh BIOS has been updated with a non-SLIC-compliant version
2) The OS is slightly corrupted in some way, and can't self-activate the Key
To properly analyse and solve problems with Activation and Validation, we need to see a full copy of the report produced by the MGADiag tool (download and save to desktop - http://go.microsoft.com/fwlink/?linkid=52012
Once saved, run the tool.
Click on the Continue button, which will produce the report.
To copy the report to your response, click on the Copy button in the tool (ignore any error messages at this point), and then paste (using either r-click/Paste, or Ctrl+V ) into your response.
- **in your own thread**, please