@Mischa1
Welcome to HP Support Community
I would like to help
I appreciate all your efforts and expertise in troubleshooting this issue
Since the BIOS Recovery did not work, using a Recovery USB Media would not be useful right now since you are unable to get past the BIOS
I suggest you contact HP Support in your region for Service Options
1) Click on this link - www.hp.com/contacthp/
2) Select your product type below.
3) Enter the serial of your device.
4) Select the country from the drop-down.
5) Select the chat or get phone number options based on your preferences.
6) Fill the web-form and proceed further.
Thank you
If the information I've provided was helpful, give us some reinforcement by clicking the "Solution Accepted" on this Post and it will also help other community members with similar issue.
KrazyToad
I Am An HP Employee