I browsed through all of the threads and didn't see a similar scenario that matches the symtoms I am facing with my Vetta II that I just purchase yesterday from Guitar Center.
While playing on the amp and modifying the preexisting patches for a tone to my likeing the sound coming out of the cab cut off abruptly and the screen froze on channel 1A. I turned the amp off and waited about 30 seconds and turned it back on. Now both of the screens are completly blank and no sound is coming out. I tried to run the flash update, but that didn't seem to work. I left the amp off for several hours and tried again and both of the screens are completly blank still and no sound is coming out of the cab.