I put in a blu ray dvd but it will not work. Help

First the smartypants answer: Make sure that you're using a Blu-Ray player. Not all PC drives are Blu-Ray either. The more likely answer: Check your Blu-Ray players manufacturer website technical support for the latest FIRMWARE. It has to be up to date with the newer DVDs. I had to update mine on my Sony unit so that Avatar would play. I went to Sonys' site and downloaded the update as an .iso file on a blank dvd. It ran and installed w. no worries. The company will also usually mail you an actual cd/dvd if you can wait and don't want to get all technical, dvd burning, etc.