Windows does not shut down or restart sometimes. I use ctrl/alt/delete and it lists internet explorer and mcafee virus scan are not letting computer shutdown. I close all programs and even exit them before shutdown. Computer gets to the windows is shutting down screen and it stalls there. If I have it set to turn off monitor or go to stand-by after certain amount of time, it will not happen. This does not happen all the time, but it is getting more frequent. What can I do?