You have already used @BIOS so using it properly should be no problem
@BIOS can flash a BIOS that you have downloaded as well so you can manually force a BIOS flash tru it.
Go on the product page choose the right version and download the BIOS file.Unzip the archive content and when trying the manual @BIOS flash point it to the BIOS file you ve unziped.
Of course it s risky ,but you already have a half working board
@BIOS ignores the checksums of the file so it s the way to restore your board.
Just make sure you remove all unneeded hardware from the config and find a way to have a fully stable system that doens t freeze.Then use the @BIOS and pray to finish successfully the flash
Otherwise a hardware store/repair shop is the solution.