Your system generating a failed POST would seem to indicate that the problem is the video card, but it still could be the motherboard or the PSU. It is also possible that you have two problems (I know, not what you wanted to hear). That is why testing your video card in another computer would be a better idea - and a bit safer.
It is possible that your motherboard ate your video card and that it would also eat another good one. Not likely, but possible.