Boot into safe mode with networking (F8 on startup). Download, install, and update malwarebytes. Do a full system scan.
While still in safe mode with networking, download ccleaner. Use the registry tool to scan for issues. Repeat the scan until it has resolved all the issues.http://www.piriform.com/ccleaner
If that doesn't solve the problem, check the event viewer to see if it's logging errors when you try to shut down.