Try a different key. I've had a couple totally ok and error free usb keys literally refusing to boot when installing Linux on a PC. Using a different usb drive solved the problem, and the dongles which refused to boot on that pc worked perfectly on different ones. I've also seen laptops which wouldn't connect to their home router WiFi no matter the settings, I had to put either an external WiFi adapter or swap the router, needless to say that both the WiFi cards and routers were 100% functional when connecting to other hardware. Some pieces of hardware just don't like talking each other.