I searched the forums for this type of problem and couldn't find it exactly...the other discussions on macbooks not sleeping involved a USB device plugged in, or something to that extent. I don't have anything plugged in, but when I close the screen, it initially goes black as the hard drive/fans are still going, then when those finally quit (starts to go into sleep mode) the screen immediately turns back on with the characteristic "screen turning on" sound. It then repeats the process (screen goes off, hard drive/fans go off, screen turns back in) like it's stuck in a loop. Any ideas?