I have a 21.5" iMac bought in November 2009. I am having a strange happening with it. I have just been using Mail, clicked on the red button at the top left to quit, but the mail window just kept disappearing all but about 3mm off the screen to the top and top left and not quitting. I have also had this happen when using Safari, occasionally if I click on a link on the page to another open another page Safari disappears off the top and top left except for about 3mm. Help please.