No, it's the drivers; the 190/191 driver lines are known to have the same intermittent black screen issue you describe.
Coincidence? Almost certainly not.
Did ya even think to try older drivers before making the warranty-voiding, logic-defying move of changing the card's bios? Hell, the card's probably screwed up forever now solely because of your inability to not panic.
I, personally, cannot wait to see what you do when you encounter your first post-jump driver quirk (and ATi have their share of those). Probably shoot it with your dad's shotgun, or something.
Could actually be kinda cool! But just so's we're clear (and I do feel as if I have to be explicit about this next point), a graphics card won't work after you do that either.
Feel better now?