Right - first of all - you only need the GPU driver - forget the other bumph that ATI try and give you go here - is this what you have Drivers & Tools | GAME.AMD.COM you want the bottom download button DISPLAY DRIVER ONLY
It says on the ATI website that this GPU requires 400Watt, I think this is being VERY safe on their part.
if you go to C:\ program files and then ATI within the ATI folder there should be some files - can you list them all please.
and we can go from there