Z390 Motherboard

Your board has the ASUS crash free bios recovery feature:
CrashFree BIOS 2
The CrashFree BIOS 2 feature now includes the BIOS auto-recovery function in a support CD. Users can reboot their system through the support CD when a bootable disk is not available and go through the simple BIOS auto-recovery process. ASUS motherboards now enable users to enjoy this protection feature without the need to pay for an optional ROM.

Your manual ought to give you the step by step instructions.

You press the Power On button. This in turn presses against the Power On switch,

http://www.directron.com/atxswitch.html

Closing the Power On switch, (Pressing the Power On button), activates the Soft Power On feature of the Power Supply.

The Power Supply comes on.
The first chipset to receive power is the BIOS chipset.

The BIOS program looks to see what devices are installed, does a Ram Memory count, turns the Processor on, and hands the computer over to the Operating System. (Windows)

BIOS will come up even with the Processor not installed. Does need the Ram Memory, though.

Post back what you mean by, "I have checked HDs...."

Do you have more than one harddrive in a RAID configuration?

Have you used a program like Memtest to check the Ram Memory?
(Sometimes it's as simple as cleaning the contact pins, on the Ram Memory modules, with a pencil eraser. Doesn't take much corrosion to make a bad contact )

Replaced the CMOS battery? Yes, sounds inane, but that watch style battery can mess up a lot of things.

Regards,
joecoolvette

You can get the BIOS flash utility at the Gigabyte website. As far as the actual flashing is concerned, it is a fairly simple and straight forward process. The specifics will depend on the utility that you download. You will need TWO things. The flash utility and the firmware you wish to install. Just a bit of warning, improper flashing of the mobo's BIOS can lead to catastrophic failure of the motherboard, so take care and follow the instructions to the letter.

http://majorgeeks.com/BIOS_Patcher_d3965.html
Find and fix errors in your system BIOS.
BIOS Patcher can find and fix errors in your system BIOS (only AWARD BIOS for now) and also it can add or open new features, i.e. some features that your BIOS has but they are closed by manufacturer of your motherboard. It scans rom file. If it finds any known errors it fixes the errors. If it finds any closed features it opens it.

go into the bios (the button to enter bios is different with different company's) but when you turn on pc it should say near the top of bottom of the 1st black screen something like "Press Delete to enter BIOS"#
from in the bios you can go to the advanced option ans just disable the on-board audio.