Hello conreHP,
Welcome to the HP Forums! I hope you enjoy your experience!
I understand the computer cannot detect an operating system. I will do my best to assist you! To troubleshoot, please follow all of the steps in this HP document: Resolve Boot Device not Found Error Message
The document suggests helpful steps such as resetting the hard drive, reset the BIOS defaults and more. If you need to reinstall the operating system, this Microsoft website contains information on multiple methods of performing this task: Installing and reinstalling Windows.
If the issue is not able to be resolved, I would contact HP phone support for assistance. You can utilize this website to learn how to contact HP appropriately, based on your region: Contact HP Worldwide
Please let me know if you have any other questions or concerns. Thanks for bringing this issue to the HP Forums. Have a great day!
Mario