I've got an Early-2008 Mac-Pro, 18GB RAM, Two Monitors (Cinema Display 30" and Cinema Display 20") and running El Capitan. I've just replaced the original Graphics Card with an ATI Radeon 5770 and the 20" Monitor doesn't wanna play-ball; there is a signal reaching the monitor but it's corrupted, it's clearly getting something but nothing that can be recognised, it's a bit of a mess. Is this a resolution issue ? if so, can anyone suggest how I can deal with it; technically, I belong in the 'Idiot' category so I'd appreciate words of one-syllable. Kind thanks, Ajaycee.