my imac is not allowing me to use full screen. the arrows in top right corner does not do the job. everything i view now has a margin of about five inches on each side and limits some of the screen size need to get back to full size screen
Have you tried a reboot? Which iMac? What Version OSX? What application is not full screen? Do you mean that you have black bars on the sides of the display, or that the application won't go to full wide? You haven't given us much to go on here.