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As I understand you are having issues with no sound when connecting using HDMI cable on your HP 27 monitor. 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:
What is the product number of this Monitor? (Ensure you do not share any of your personal information such as serial, phone number, email ID, etc...) http://hp.care/2bygf7l
Does this monitor have internal speakers?
Have you tried changing the audio configuration in the control panel?
Reinsert the HDMI cable into the HDMI port on the notebook PC.
After approximately 10 seconds, switch the audio source in the Control Panel:
Click Start, Control Panel, Hardware and Sound and then click Sound.
Select the HDMI audio device, click Set Default and then click OK.
Since there would be no sound from the computer speakers or headphones because HDMI transfers the sound to the monitor speakers.
In this scenario, you can use a DVI cable or change the playback settings to play in speaker instead of HDMI to change the speaker settings.
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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As I understand your monitor does not have internal speakers, I would suggest you try to check by connecting an external speaker or a headphone to your Lenovo laptop and check if it works, If you are able to hear sound from the external speakers or headphones, I would suggest you contact Lenovo tech support for further assistance.
I hope this helps. Let me know how it goes for further assistance.