Menubar is not updating based on active application.

Hi,I am using iMac with 10.7.4 mac os.My problem is menubar is not updating based on active application.And finder menu bar is appearing when i open the finder.And on thta time if i select "About my mac" or "Force quit" then that didn't give any response.At same time when i open any application like firefox or anything that finder menu bar is apper but not responding.And another probelm is at the time of login i entering the password and submitting,it's opening the desktop and again total screen will be becpme white and showing the activityindicator.Sp please tell me what's the main problem.And how can i solve these problems.