Greetings,
With the PSU disconnected, and MB battery left installed, try to reset your CMOS. Believe your board only has a jumper.
Remove your GPU if installed and connect directly to onboard graphics. Retest
**Optional step is to reseat all peripherals and connections. Also bench test, but the fact that it was working and then stopped means this would be less likely to help or provide more information about the failure.
And, finally, try invoking boot from the back up BIOS. Unfortunately, without any power up activity, the board could be dead, but if doing the above steps doesn't help, you'll know you gave it your best effort.
Good Luck