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I understand you are having an issue with the keyboard not working on your new HP Wireless mouse x4000 with a laser sensor. Don't worry as I have a few steps to help you get through this concern,
To provide you with an accurate solution, I'll need a few more details:
Did you purchase the Wireless keyboard and mouse as a bundle or separate?
Have you tried to synchronize the keyboard the mouse?
In the meantime, If this keyboard is not bundled and purchased separately, this could be one of the reasons why the keyboard is not working.
If this is bundled, I would suggest you try to synchronize the keyboard and the mouse, using this link.
I hope this helps. Let me know how it goes for further assistance.
Please respond to this post with the result of your troubleshooting. I look forward to hearing from you.
If you wish to help others looking for the same solution as you've found, mark the post as Accepted Solution.
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