Xbox360 that doesn't know it is one

I had the same problem,If it is under warranty send it in ,,, if not then you are going to open it up,, plenty of instruction on how to do this online (google it). see what type of dvd drive you have and then go on ebay and purchase an identical replacment drive. once you recieve it open up YOUR ORIGINAL DVD DRIVE and unplug the green motherboard looking thing on top(Big ONE) there should be four little tabs on this. put it to the side . now open up the new dvd drive and repeat but make sure you dont get these cards switched up.put the old key in the new dvd drive , plug in all 4 tabs,bottom one first. put back together and install back into xbox360. put xbox 360 back together put in disk and enjoy