Try switching your computer off. I'm not sure if you have a desktop PC but if you have remove the side panel and disconnect the leads from the DVD drive, replace the cover and then switch the PC on and see if it finds and installs it.
Try running CheckDisk (ChkDsk). Go to My Computer>right click>Explore>highlight your optical drive>right click>Properties>click on Check for Errors button>tick the first box (second as well if you wish to check for sector errors)>OK and then immediately Reboot.
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