Installed Ubuntu 13.10 from DVD to my Hard Drive. Software installed successfully. Screen said to restart computer. DVD door opened to give me disk. I restarted computer (Dell Vostro 1500) Computer offered choice of Windows XP or Ubantu. I chose Ubantu. Ubantu tried to start from Hard drive, but failed. Screen wanted DVD reinserted to run. Why can't Ubantu run solely from HD? What do I need to do to make it run just from the HD where it was installed?