Is this in a desktop or laptop configuration. The HD7400 is only available in a HD7400M model.
based on the limited information you have given you may one of those out of luck if your running Windows 10. Many have had to revert to Windows 7 to get the 7400m to work again. Some find they have no way to disable the legacy gpu in the bios and Windows 10 installs an incorrect driver automatically. I have no personal experience with this, yet have seen ray_m who replied above speak about this many times. Maybe if he thinks this might be the case he could explain it better to you! Good luck!