Have a USB stick or DVD with a bootable operating system ready.
Insert the USB stick into a free USB port or insert the DVD into the drive.
Power on or restart the device.
As soon as the manufacturer's logo appears, immediately press the boot menu key.
Acer: F12
ASUS: Esc or F8
Dell: F12
HP: Esc, then F9
Lenovo: F12 or Enter
MSI: F11
Gigabyte: F12
Medion: F10 or F8
Packard Bell: F8 or F12
In the boot menu, use the arrow keys to select the USB stick or DVD drive.
Confirm with Enter.
The system will now boot from the selected medium.
Either a live environment or an installer will start.
Enter the BIOS/UEFI (usually by pressing F2, Del, or Esc at startup).
Navigate to the "Boot" menu.
Move the USB stick or DVD to the top of the list.
Save changes (usually F10) and exit the BIOS.
USB stick not recognized: Try a different port (preferably USB 2.0).
Check if the medium is truly bootable.
Disable UEFI/Secure Boot in the BIOS if necessary.