I would like to know some information about the issue so that we could help you better.
What is the model number of your HP touchscreen computer?
I appreciate you for providing details about the issue.
I also realize the inconvenience you are experiencing due to brightness issue. I will certainly help you.
This issue may occur due to corrupt or incorrect power and display settings.
I would suggest you to try following methods and check if it helps.
Please run this Microsoft fixit and check.
If it does not help, use method 2.
Please use steps provided in this article and check the issue.
Get the best display on your monitor
I hope this information helps.
Please do let us know if you need any further assistance.