Hello and welcome to the forums. Sorry to hear about your troubles.
I would suggest trying to clear the cmos. First power off the system, switch off the psu and remove the power cord from the back. On the motherboard press and hold the clr cmos button for 5 - 10 sec. Reconnect everything When you power on you should be presented with a screen with a couple of options. One of those should be to load optimized defaults and reboot. Choose that and see if you can enter bios. If not one of the other options is to enter setup which is the bios, choose that. Once in press ESC key to exit out of 3d mode, go over the last menu on the right and scroll down and chose load optimized defaults. Before saving changes make sure usb keyboard and mouse support are set to enabled, Dont make any other changes at this time. Try to renter bios again, if you can make any further changes need or maybe at this point update bios if need which is most likely.
You can find the must up to date bios for your board here GIGABYTE Latest Beta BIOS
Also if you are using a dedicated gpu, you must connect the monitor to that to be able to see bios splash screen.
Thank you for providing a detailed list of your hardware and filling out your PC specs.