multi boot – How to enter BIOS menu?

Laptop Fujitsu LH532.

After an unsuccessful attempt to install Arch Linux, I cannot enter the BIOS menu of the laptop. It just beeps, power keeps being on, but it doesn’t load anything and does not provide any output.

During the Linux installation, I played a bit with the EFI partition of the HDD and removed several old boot entries with efibootmgr, but that’s it.

Before there was Windows on this laptop and again instead of BIOS after F2/F12 I arrived to some windows loader menu.

Now I cannot load from a USB drive and I have only access to half-dead Linux, but the system console is operational.

How can I understand what is going on and how to make the machine able to boot from a flash drive?