I get a message that says to reboot when I turn on my laptop.

When I turn on my laptop the Toshiba logo comes out as normal but then it turns all black and a message comes out that says “reboot and select proper boot device or insert boot media in selected boot device and press a key”. I have tried several things. There was one method that worked for many people and it was to go to the bios menu, disable the secure boot then go to system configuration and change the boot mode from Uefi to csm. I went to the bios menu and disabled the secure boot but when I go system configuration the boot mode tab does not even show up. I have no idea how to fix my laptop please help.