Missing a 12v cable? Does your PSU have a 20-pin ATX connector? If true, either purchase a 24/20 - pin adapter or purchase a PSU with support for a 24-pin ATX interface. Unless your taxing the PCI-E with a video card or another process-intensive load on that line, you don't need the 12V connector. If this system sounds like yours, purchase an adapter and make sure your PSU is up to snuff, as only the first 20 pins provide power. If not, I recommend a newer PSU, innately supporting 24-pins out of the box. I'm probable some people might argue that a old monster quality PSU could support the latest and greatest PCIe graphic cards, but this is my recommendation; so, please feel free to absorb other advice.