Why my acer laptop is not shutting down?

Hi guys my Acer E series laptop is not responding whenever I want to close it that is whenever I click on shut down it is not at all responding its just happening since 2 days though I did not make any changes in my laptop.My Acer laptop is E series 512 and runs on Windows 7 operating system. Please help me solve this problem as I can shutdown it by using switch user and then selecting shut down but not directly.
