Help! Dreamcast Bricked! :(

[SWAT]

You can try restore factory settings in FlashROM by Region Chanager app.
Make backup on working DC and restore it on broken.

But this failure could mean that the life of your FlashROM just ended, as all the games permanently write some data to it (damn, they do a lot of writing there!).
So in this case you help only replacement of this chip.

As a note. If you broke the BiosROM, the console would not boot at all, so it's not your incident.