@Slurfer
I'm sorry, but HP only warranties their PCs for usage with the OS that comes preinstalled.
IF you replace that with a Linux distro, or add a Linux distro, then you assume full responsibility for maintaining that -- including solving any problems with booting the other OS and/or installing the other OS.
Modern PCs with UEFI, instead of the older BIOS, are especially difficult to install because you have to go into the UEFI settings and make several changes before you can even boot from a USB stick -- and we are unable to assist in that work.
Your best bet for support now is to contact the support forum of the distro you are using.
Good Luck
I am a volunteer and I do not work for, nor represent, HP