I want to install ubuntu on my windows tablet pc. I already prepared a boot usb, but I can't select the usb to boot in bios. (see image) Perhaps i could boot from usb in the built in UEFI Shell? Thanks for your help! I can't post an image because I have too less reputation.
SnapOverflow
You need to look if your bios will let you enable "Legacy" boot.
Check if "Secure Boot" is on (needs to be off).
Check if there is a restricion in place for booting from USB. Check if "Legacy USB" is activated.
There might even be a key combo that lets you select where to boot from while startup.
Without really seeing where you are stuck I am just throwing some guesses which may be available to you or not.