my macbook air will not restart

Something is interfering with the shutdown process. Hold the power button for a slow 10 count. That will shut down the computer. Then you can click the power button to restart it. Whenever I have to do a forced shutdown I run Disk Utility and then select Disk First Aid to make sure there was no damage to the file system. If an error pops up don't panic. Restart holding the Command & R keys and then select Disk Utility and run Disk First Aid again. This should fix any errors that were found.