WTF?
Seems XFX removed the bios switch on
these cards! (5:10)
So you may be screwed.
With not being able to use your 2500k's video to boot, I'm not even sure you can do a "blind flash".
Since i'm pretty sure your pc wont even post with a bad video card bios.
I wouldn't try flashing with the HD 5770 in there, you may end up messing up its bios also since its AMD also.
EDIT: I wonder if you can enable the 2500k video and get it to post with no monitor hookup and try and flash back "blind" with a bootable USB stick.
BTW: IMO XFX are some cheap mofos for saving a few cents by not including a 2nd backup bios like all other 7950's.
If you can RMA it, I personally would sell the new card and never buy XFX again, since IMO this alone says a lot about how they feel about offering a quality product.
Makes ya wonder where else they cut corners on their cards.