Wait, it worked with a 4870x2? The 4870x2 eats way more power then the 5770. I would asume that its the card, defective card. Also make sure the power is plugged into the card. If it works with another ATI card, they I don't see why it would with another, unless the PSU is screwed, try a different 1 you can. rule that out of the way.