|Ye that's the psu.|
So, this is what I've done:
1. Received the video card, but I couldn't use it since my psu didn't have these 6-pin cables.
2. I got the new psu, put it into the computer and left my old video card inside, worked perfectly.
3. Replaced my old video card with the xfx 6870, the screen won't detect any signal. It's all black...
I don't really know what you mean with a POST beep from the motherboard.. but I don't think so :P