Dell inspiron 15r bios access is usually helpful when you would want to choose the configuration of your choice and that you face issues that in reality become obstacle in laptop functioning.
If you are trying to access from CD or DVD, make sure the respective drive is set to boot priority. You should be seeing a splash screen that asks you to press F2 key in order to access the bios menu.
If this does not work, you could also try pressing other key combinations like DEL, esc +alt, and variations of such keys with F12.
The bios related stuff and safe mode can simply be accessed through the dell inspiron 15r bios access at the very beginning of your laptop reboot.