I cannot remove sure boot. When I do, the PC reboots without secure boot. I have found an answer: turn on display post messages in the bios. And then turn of secure boot. Save and exit. The Bios will show a message like: "a Secure boot turnoff is pending. Type the folowing caracters and then ENTER at the keyboard. After that the secure boot option is turned off.
That's it. Hope it help someone.