No jump to BIOS possible with bootable media?

I have currently noticed an interesting effect on my ASUS G750JH notebook: When I start the computer and want to call up the BIOS, the optical drive that has been installed since the beginning is no longer displayed as a boot option (with the I / O devices however, it is listed together with the installed hard drives). If I insert a bootable disc into the drive (e.g. GParted or Acronis), the computer hangs before jumping into the BIOS and does nothing. The same thing happens when I plug in a USB stick with bootable software. Therefore I can no longer carry out any system restoration.

My questions in this context:

- Has anyone here in the forum already encountered a similar effect, and if so, how did he / she solve it?

- Can someone tell me here in the forum whether there's a virus that could produce such an error? I installed Bitdefender on my computer and it didn't report anything. Otherwise the computer has been running smoothly so far; I can't detect any increased data traffic and also see nothing abnormal in the Task Manager or in the processes.

- Does anyone know another workaround here in the forum, with which I can bring my system back so that it can be started from bootable media? Connecting an external drive also did not work.

- Is there a setting in the BIOS that I could accidentally activate and that leads to the effect described?

- Is there a function in Bitdefender that I could have accidentally switched on and that causes the described effect (as a security feature, so to speak)?

I would be really grateful for answers to my questions.

Yes there's, see the BIOS / UEFI under Security. There's an option there that prevents you from booting from another external medium.

Hm - the BIOS is from 2013 and has no graphical interface at all, as it would be common today (but of course it can be that one has nothing to do with the other). But I will follow the lead at the next opportunity and report…