I just built a custom PC today, and everything is going without a hitch except for the graphic card (ASUS HD 7770). When my computer doesn't have the graphic card inside, it can display just fine via its onboard graphic chip. When I plug in the card, I get an 'Invalid Format' error message on my TV screen. I've searched the forums but other people's issues seem to be because they've set the resolution outside their monitor's capabilities; I can't even change my resolution because I can't see nor change anything with the card inside.
The computer turns on, and all fans are spinning. There's a LED on the graphic card and it glows green when plugged in, so I don't think there's anything wrong with it. But, for completion's sake, there was a moment when I turned on the power to my computer without plugging the power in to my graphic card (so it was only connected via PCIe). The light was red for that moment before I quickly turned off the computer.
Plugging in the power to the card and turning on the computer won't damage anything. You are going to have to change the format of your video output. You should plug a monitor, if you have one, into one output on the card and plug your TV into the other. More than likely your monitor will be able to handle the format so you can see when you change the format on the TV. To change the format on the tv you would have to go into the Catalyst control center. On the left pane you will see digital flat panel. Choose the format that your TV says it can handle with HDMI.
Hopefully this helps