Hello markpf189,
Thank you for posting on the HP Forums!
I understand you cannot disable the brightness of a certain key. I will do my best to assist you!
This could be a hardware issue, to be honest. However, you should make sure that all of the computer's proper drivers are installed. You can use the HP Support Assistant to install the proper drivers. For more information on how to do this, please reference this HP document: Downloading or Updating Software and Drivers for HP Computers
If this does not resolve the issue, then there is probably a hardware issue. Please let me know your results. Thanks for choosing the HP Forums. Have a great day!
Mario