Older board, don't recall if it has a flash back port and button on the I/O panel. Pretty sure it doesn't.
Disconnect the 24 pin power connector. Then use a jumper or flat blade screw driver to short the CLR_CMOS jumper (lower right corner) of your board. 10 sec should be enough. No reconnect the power and start the system. Start tapping the <DEL> key. Tap, pause, tap pause to enter BIOS... result?
If this doesn't work, you should attempt to start the system and invoke boot from the back up BIOS.
If you are using a wireless keyboard, change for a wired keyboard during troubleshooting.
If you are connecting to a TV or using an adapter or any kind, test using a standard computer display and cable connected directly without adapter.
If all of the above fails, remove the GPU, (use on board display), remove all RAM except one stick, perform a CLR_CMOS described above and attempt to start the system.
The fact that you were able to enter BIOS after an unsuccessful flash and load set up defaults is a good sign. Hopefully one of the above actions will recover the system and allow you to enter BIOS and reconfigure your Boot Order and configuration.
Please post your progress.