I;m having a problem that started after i did a PRAM reset. When i turn on my white unibody macbook 2009 model I hear the chime but the screen stays black, after some time I'm presented with the log in screen of the os. The machine works fine once the os loads but weirdly doesn't show the apple screen at start up any more. Please help as Ive searched the net for the last three days finding nothing like this issue