Turn off the computer by pressing the Power button on the case, and turn it back on. Press the function key Del to go into BIOS mode. Please note that depending on model can use other function keys - F2, or F10. Specific key is usually indicated at the bottom of the screen - in line Press ... to enter SETUP. You may also need to press the desired key several times.
In AMI BIOS, you can go to the Boot tab in the top toolbar, using the arrow keys up and down and confirm your choice pressing the function key Enter. Then expand the Boot Device Priority and select the line 1st Boot Device. Press Enter and select the line CDROM in the Options section. Confirm changing download settings, once again press Enter, and use the function key Esc to exit the boot menu. Go to the Exit tab top window panel BIOS and click on the OK button in the opened window of the query saving the changes made. Wait for the automatic reboot and make sure that the operating system is loaded from disk.
If the computer uses the Award Bios, select Advanced BIOS Features in the left pane of the window with the arrow keys and press the function key Enter. Select the line First Boot Device and confirm your choice by pressing the Enter key. Specify the CDROM item in the opened submenu the boot device and select Save and Exit Setup in the main window. Save the made changes by pressing Y in the opened window prompted, and wait for the reboot to be executed in automatic mode.