I just recently purchased a nividia 7900 GTX (used). From the outside it seems to be fine, nothing wrong. However when I any games on it, it is not play correctly. It is either not loading the full image, or it flashes to black and back to normal quickly. I sometimes get vertical or horizontal lines that appear. I am lead to believe that it is not getting enough power. I am using a 350W power supply. Is this the issuse?