|Del is the correct key to press to get into the bios, if it's a generic desktop system, which normally has a retail (Asus) mboard model.|
If it's an Asus mboard that came with a brand name system, it's the brand name's specified key, never Del. See The Owner's or User's manual for the brand name model if the key is not stated on the screen while booting.
You must press the key repeatedly while booting, do not hold down the key, starting very early in the boot sequence . You may need to start pressing the key right after the led on the monitor turns green (or whatever color it is when the monitor has video in Windows).
You can always get into the bios with a PS/2 connected keyboard.
Is your keyboard connected via a USB plug ?
If yes, you can't get into the bios with a USB connected keyboard unless Legacy USB or similar is enabled in the bios Setup.
Older bioses often have that setting disabled by default - newer bios often have that enabled by default.
If that setting is disabled, if you have or can borrow a PS/2 keyboard, connect that when the computer is NOT running, boot the computer and go into the bios and change the Legacy USB or similar setting to Enabled, Save settings. Then a USB keyboard will get you into the bios.
If you don't have or can't borrow a PS/2 keyboard.....
If your mboard is a retail model, see your mboard manual - Asus manuals usually show you which settings are the default settings..
If the default is for that setting to be enabled, then you can remove the cmos battery on the mboard, install it again with the + on it visible when it's installed, or move the clear cmos jumper to the clear position, move it back, then a USB keyboard will get you into the bios.
However, in both cases, you will get a CMOS Checksum Error or similar when you boot, and you need to go into the bios Setup and set at least the date and time, Save settings.